Computer System Applications: Design and Development
Laboratory Manual
Dr Mohammad Jahangir Ikram
Department of Computer Science
Lahore University of Management Sciences
Table of Contents and List of Experiments
1. Data Input and Output Using Parallel Port
1.1.
1.2.
1.3.
1.4.
1.5.
2.
3.
4.
5.
6.
7.
Introduction
The Theory of Parallel Port
The Circuit Diagram and Parallel Port Addressing
Programming Languages Support for Data input and Output using Parallel Port
The INPUT/OUTPUT Experiment
1.5.1.
The OUTPUT experiment
1.5.1.1.
Theory and Circuit Diagrams for Experiment 1
1.5.1.2.
Programming Project: The Roulette Wheel
1.5.2.
The INPUT Experiment
1.5.2.1.
Circuit Diagrams
1.5.2.2.
Study of Basic Input
1.5.2.3.
Study of Key Debounce
1.5.2.4.
Study of Nibble-Mode Input
1.5.2.5.
Programming Project: The Printer Status Emulator
Programming of Display Matrix
2.1.
Introduction
2.2.
The Theory And Circuit Diagrams For Display Matrix
2.3.
Fundamental Operation
2.4.
Time-Multiplexing Techniques for Display Matrix
2.5.
Displaying a Character
2.6.
Programming Project: The Snake and Marshmallows
The A/D and D/A Conversion
3.1.
Introduction
3.2.
The Digital to Analog Conversion
3.2.1.
The Basic Conversion and Study of Quantization Error
3.2.2.
Waveform Generation
3.3.
The Analog to Digital Conversion
3.3.1.
Study of Basic Conversion
3.4.
Programming Project: FFT Analysis
The Motor Speed Measurement and Control
4.1.
Introduction
4.2.
Basic Measurement
4.3.
Using of Data Acquisition Techniques
4.3.1.
Array Filling
4.3.2.
Interrupt Control
4.3.3.
DMA
Temperature Measurement and Control
5.1.
Introduction
5.2.
Basic Control Techniques
5.2.1.
ON/OFF Control
5.2.2.
Variable Control
5.3.
Loose and Tight Control: Advantages and Disadvantages
Interrupt Programming
6.1.
Introduction
6.2.
Basic Programming
6.3.
A simple hardware Interrupt based TSR
A simple Device DOS Device Driver for Motor Speed Control
The block diagram of the LUMS Parallel Port Interface Board (LPPIB) is given on next page.
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Dr Mohammad Jahangir Ikram
LEDs
ADC
0804
Analog to Digital
Connector
Power
Supply
Section
Kick
Start
Switch
0-5 V
Analog
DIP SWITCH
Connector
747 Dual
Op Amp
Sensor
O/P
From Variable Power Supply
LUMS Parallel Port Interface Board
Analog
I/P
MOTOR
EN
74244
as
MUX
+5
Analog
Output
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2
4
5
6
7
8
9
Input
Port
8 X 8 Matrix Display
Output Port
3
DB-25 Connector to
Computer Parallel Port
Resistors
LEDs
1, 14 (for
Row/
Coloumn
Select)
Row
Latch
Coloumn
Latch
Matrix Connector
1,14 (O/P)
Digital to Analog
Connector
Computer System Applications: Design and Development
Laboratory Manual
Dr Mohammad Jahangir Ikram
Department of Computer Science
Lahore University of Management Sciences
Read Laboratory Notes carefully before you come to the class.
Chapter 1:
Contents
1.
2.
3.
4.
5.
6.
Introduction
The Theory of Parallel Port
The Circuit Diagram and Parallel Port Addressing
Programming Languages Support for Data input and Output using Parallel Port
Theory and Circuit Diagrams for Experiment 1
Programming Assignment
1. Introduction
The Computer System Applications (CSA) course has extensive laboratory workload. A special
hardware board has been designed to do a list of experiments. The list is as follows:
1.
2.
3.
4.
5.
6.
7.
Study of Parallel port and I/O through Parallel port
Programming a Display Matrix
A/D and D/A Conversion
Motor Speed Measurement & Control
Interrupt Programming
Speed Control Using Interrupts
Device Driver Programming
The board can be attached to the printer port of any computer and can be programmed in any
software, namely, DEBUG, Pascal, C, C++, Qbasic and Visual Basic etc. In the laboratory two
students are assigned to a single board and some boards may be available for issuing to
students for experimenting at home.
First we study the theory (history, circuit design, programming methods) of a parallel port. Then
the experiments are discussed that you are going to perform on the first day of the lab.
The main purpose of the lab is to provide students with some hands-on experience with the
interfacing.
Parallel port is not the only way to interface a computer with the outside world, a special plug-in
card can also be used. This method is discussed in last experiment in the above list.
2. The Theory of Parallel Port: Programming, Interfacing, & Using the PC’s
Parallel Printer Port
A first step in exploring the parallel port is learning how to get the most from a port with your
everyday applications and peripherals. Things to know include how to find, configure, and install a
port, how and when to use the new bidirec-tional, EPP, and ECP modes, and how to handle a
system with multiple parallel- port peripherals. This chapter presents essential information and
tips relating to these topics.
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21. Defining the Port
What is the “parallel port”? In the computer world, a port is a set of signal lines that the
microprocessor, or CPU, uses to exchange data with other components. Typical uses for ports
are communicating with printers, modems, keyboards, and displays, or just about any component
or device except system memory. Most computer ports are digital, where each signal, or bit, is 0
or 1. A parallel port transfers multiple bits at once, while a serial port transfers a bit at a time
(though it may transfer in both directions at once).
We are talking about a specific type of parallel port: the one found on just about every PC, or
IBM-compatible personal computer. Along with the RS-232 serial port, the parallel port is a
workhorse of PC communications. On newer PCs, you may find other ports such as SCSI, USB,
and IrDA, but the parallel port remains popular because it’s capable, flexible, and every PC has
one.
The original PC’s parallel port had eight outputs, five inputs, and four bidirectional lines. These
are enough for communicating with many types of peripherals. On many newer PCs, the eight
outputs can also serve as inputs, for faster communications with scanners, drives, and other
devices that send data to the PC.
The parallel port was designed as a printer port, and many of the original names for the port’s
signals (PaperEnd, AutoLineFeed) reflect that use. But these days, you can find all kinds of things
besides printers connected to the port. The term peripheral or peripheral device is a catch-all
category that includes printers, scanners, modems, and other devices that connect to a PC.
2.2 Port Types
As the design of the PC evolved, several manufacturers introduced improved versions of the
parallel port. The new port types are compatible with the original design, but add new abilities,
mainly for increased speed. Speed is important because as computers and peripherals have
gotten faster, the jobs they do have become more complicated, and the amount of information
they need to exchange has increased. The original parallel port was plenty fast enough for
sending bytes representing ASCII text characters to a dot-matrix or daisy-wheel printer. But
modern printers need to receive much more information to print a page with multiple fonts and
detailed graphics, often in color. The faster the computer can transmit the information, the faster
the printer can begin processing and printing the result.
A fast interface also makes it feasible to use portable, external versions of peripherals that you
would otherwise have to install inside the computer. A parallel-port tape or disk drive is easy to
move from system to system, and for occasional use, such as making back-ups, you can use one
unit for several systems. Because a backup may involve copying hundreds of Megabytes, the
interface has to be fast to be worthwhile.
Let us first discuss the new port types in detail, but for now, here is a summary of the available
types:
2.2.1 Original (SPP)
The parallel port in the original IBM PC, and any port that emulates the original port’s design, is
sometimes called the SPP, for standard parallel port, even though the original port had no written
standard beyond the schematic diagrams and documentation for the IBM PC. Other names used
are AT-type or ISA-compatible.
The port in the original PC was based on an existing Centronics printer interface. However, the
PC introduced a few differences, which other systems have continued. SPPs can transfer eight
bits at once to a peripheral, using a protocol similar to that used by the original Centronics
interface. The SPP doesn’t have a byte-wide input port, but for PC-to-peripheral transfers, SPPs
can use a Nibble mode that transfers each byte 4 bits at a time. Nibble mode is slow, but has
become popular as a way to use the parallel port for input.
Note: Our Experimentation will be limited to SPP mode
2.2.2 PS/2-type (Simple Bidirectional)
An early improvement to the parallel port was the bidirectional data port introduced on IBM’s
model PS/2. The bidirectional port enables a peripheral to transfer eight bits at once to a PC. The
term PS/2-type has come to refer to any parallel port that has a bidirectional data port but doesn’t
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support the EPP or ECP modes described below. Byte mode is an 8-bit data-transfer protocol
that PS/2-type ports can use to transfer data from the peripheral to the PC.
2.2.3 EPP
The EPP (enhanced parallel port) was originally developed by chip maker Intel, PC manufacturer
Zenith, and Xircom, a maker of parallel-port networking products. As on the PS/2-type port, the
data lines are bidirectional. An EPP can read or write a byte of data in one cycle of the ISA
expansion bus, or about 1 microsecond, including handshaking, compared to four cycles for an
SPP or PS/2-type port. An EPP can switch directions quickly, so it’s very efficient when used with
disk and tape drives and other devices that transfer data in both directions. An EPP can also
emulate an SPP, and some EPPs can emulate a PS/2-type port.
2.2.4 ECP
The ECP (extended capabilities port) was first proposed by Hewlett Packard and Microsoft. Like
the EPP, the ECP is bidirectional and can transfer data at ISA-bus speeds. ECPs have buffers
and support for DMA (direct memory access) transfers and data compression. ECP transfers are
useful for printers, scanners, and other peripherals that transfer large blocks of data. An ECP can
also emulate an SPP or PS/2-type port, and many ECPs can emulate an EPP as well.
2.2.5 Multi-mode Ports
Many newer ports are multi-mode ports that can emulate some or all of the above types. They
often include configuration options that can make all of the port types available, or allow certain
modes while locking out the others. An example is IEEE 1284 parallel port described separately
later in the chapter.
2.3 System Resources
The parallel port uses a variety of the computer’s resources. Every port uses a range of
addresses, though the number and location of addresses varies. Many ports have an assigned
IRQ (interrupt request) level, and ECPs may have an assigned DMA channel. The resources
assigned to a port can’t conflict with those used by other system components, including other
parallel ports
2.3.1 Addressing
The standard parallel port uses three contiguous addresses, usually in one of these ranges:
3BCh, 3BDh, 3BEh
378h, 379h, 37Ah
278h, 279h, 27Ah
The first address in the range is the port’s base address, also called the Data register or just the
port address. The second address is the port’s Status register, and the third is the Control
register. EPPs and ECPs reserve additional addresses for each port. An EPP adds five registers
at base address + 3 through base address + 7, and an ECP adds three registers at base address
+ 400h through base address + 402h. For a base address of 378h, the EPP registers are at 37Bh
through 37Fh, and the ECP registers are at 778h through 77Fh. On early PCs, the parallel port
had a base address of 3BCh. On newer systems, the parallel port is most often at 378h. But all
three addresses are reserved for parallel ports, and if the port’s hardware allows it, you can
configure a port at any of the addresses. However, you normally can’t have an EPP at base
address 3BCh, because the added EPP registers at this address may be used by the video
display.
IBM’s Type 3 PS/2 port also had three additional registers, at base address +3 through base
address + 5, and allowed a base address of 1278h or 1378h. Most often, DOS and Windows
refer to the first port in numerical order as LPT1, the second, LPT2, and the third, LPT3. So on
bootup, LPT1 is most often at 378h, but it may be at any of the three addresses. LPT2, if it exists,
may be at 378h or 278h, and LPT3 can only be at 278h. Various configuration techniques can
change these assignments, however, so not all systems will follow this conven-tion. LPT stands
for line printer, reflecting the port’s original intended use. If your port’s hardware allows it, you can
add a port at any unused port address in the system. Not all software will recognize these nonstandard ports as LPT ports, but you can access them with software that writes directly to the port
registers.
2.3.2 Interrupts
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Most parallel ports are capable of detecting interrupt signals from a peripheral. The peripheral
may use an interrupt to announce that it’s ready to receive a byte, or that it has a byte to send. To
use interrupts, a parallel port must have an assigned interrupt-request level (IRQ).
Conventionally, LPT1 uses IRQ7 and LPT2 uses IRQ5. But IRQ5 is used by many sound cards,
and because free IRQ levels can be scarce on a system, even IRQ7 may be reserved by another
device. Some ports allow choosing other IRQ levels besides these two.
Many printer drivers and many other applications and drivers that access the parallel port don’t
require parallel-port interrupts. If you select no IRQ level for a port, the port will still work in most
cases, though sometimes not as efficiently, and you can use the IRQ level for something else.
2.3.3 DMA Channels
ECPs can use direct memory access (DMA) for data transfers at the parallel port. During the
DMA transfers, the CPU is free to do other things, so DMA transfers can result in faster
performance overall. In order to use DMA, the port must have an assigned DMA channel, in the
range 0 to 3.
2.4 Finding Existing Ports
DOS and Windows include utilities for finding
existing ports and examining other system
resources. In Windows 95, click on Control Panel,
System, Devices, Ports, and click on a port to see
its assigned address and (optional) IRQ level and
DMA channel. In Windows 3.1 or DOS, you can
use Microsoft’s Diagnostic (msd.exe) to view
ports, assigned IRQ levels, and other system
details.
2.5 Configuring
The parallel port that comes with a PC will have an
assigned address and possibly an IRQ level and
DMA channel. Multi-mode ports may also be
configured with specific modes enabled. You can
change some or all of these assignments to match
your needs. If you’re adding a new port, you need
to configure it, making sure that it doesn’t conflict
with existing ports and other resources.
2.5.1 Port Options
There is no standard method for configuring a port. Some ports, especially older ones, use
jumper blocks or switches to select different options. Others allow configuring in software, using a
utility provided on disk. A port on a system mother-board may have configuration options in the
system setup screens (the CMOS setup) that you can access on bootup. On ports that meet
Microsoft’s Plug and Play standard, Windows 95 can automatically assign an available port
address and IRQ level to a port.
Check your system or port’s documentation for specifics on how to configure a port. Some ports
allow a choice of just one or two of the three conventional base addresses. A few allow you to
choose any uncommitted address, including non-standard ones. On some boards, the jumpers or
switches are labeled, which is extremely handy when you don’t have other documentation (or
can’t find it). If your port supports ECP transfers, assign it an IRQ level and DMA channel if
possible. Most ECP drivers do use these, and if they’re not available, the driver will revert to a
slower mode.
2.5.2 Multi-mode Ports
Configuring a multi-mode port needs special consideration. A multi-mode port’s controller chip
supports a variety of modes that emulate different port types. In addition to the configuration
options described above, on most multi-mode ports, you also have to select a port type to
emulate. The problem is that there is no single standard for the basic setup on the controller
chips, and there are many different chips! Usually the setup involves writing to configuration
registers in the chip, but the location and means of accessing the registers varies. For this
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reason, every port should come with a simple way to configure the port. If the port is on the
motherboard, look in the CMOS setup screens that you can access on bootup. Other ports may
use jumpers to enable the modes, or have configuration software on disk. The provided setup
routines don't always offer all of the available options or explain the meaning of each option
clearly. For example, one CMOS setup I’ve seen allows only the choice of AT or PS/2-type port.
The PS/2 option actually con-figures the port as an ECP, with the ECP’s PS/2 mode selected, but
there is no documentation explaining this. The only way to find out what mode is actually selected
is to read the chip’s configuration registers. And although the port also supports EPP, the CMOS
setup includes no way to enable it, so again, accessing the configuration registers is the only
option. If your port is EPP- or ECP-capable but the setup utility doesn't offer these as choices, a
last resort is to identify the controller chip, obtain and study its data sheet, and write your own
program to configure the port. The exact terminology and the number of available options can
vary, but these are typical configuration options for a multi-mode port:
SPP. Emulates the original port. Also called AT-type or ISA-compatible.
PS/2, or simple bidirectional. Like an SPP, except that the data port is bidirec-tional.
EPP. Can do EPP transfers. Also emulates an SPP. Some EPPs can emulate a
PS/2-type port.
ECP. Can do ECP transfers. The ECP’s internal modes enable the port to emulate an SPP or
PS/2-type port. An additional internal mode, Fast Centronics, or Parallel- Port FIFO, uses the
ECP's buffer for faster data transfers with many old-style (SPP) peripherals.
ECP + EPP. An ECP that supports the ECP’s internal mode 100, which emulates an EPP. The
most flexible port type, because it can emulate all of the others.
2.5.3 Drivers
After setting up the port’s hardware, you may need to configure your operating system and
applications to use the new port.
For DOS and Windows 3.1 systems, on bootup the operating system looks for ports at the three
conventional addresses and assigns each an LPT number.
In Windows 3.1, to assign a printer to an LPT port, click on Control Panel, then Printers. If the
printer model isn’t displayed, click Add and follow the prompts. Select the desired printer model,
then click Connect to view the available ports.
Select a port and click OK, or Cancel to make no changes.
In Windows 95, the Control Panel lists available ports under System Properties, Device Manager,
Ports. There’s also a brief description of the port. Printer Port means that Windows treats the port
as an ordinary SPP, while ECP Printer Port means that Windows will use the abilities of an ECP if
possible. To change the driver, select the port, then Properties, Driver, and Show All Drivers.
Select the driver and click OK. If an ECP doesn't have an IRQ and DMA channel, the Windows
95 printer driver will use the ECP’s Fast Centronics mode, which transfers data faster than an
SPP, but not as fast as ECP. The Device Manager also shows the port’s configuration. Select the
port, then click Resources. Windows attempts to detect these settings automatically. If the
configuration shown does not match your hardware setup, deselect the Use Automatic Settings
check box and select a different con-figuration. If none matches, you can change a setting by
double-clicking on the resource type and entering a new value. Windows displays a message if it
detects any conflicts with the selected settings. To assign a printer to a port, click on Control
Panel, Printers, and select the printer to assign. Parallel-port devices that don’t use the Windows
printer drivers should come with their own configuration utilities. DOS programs generally have
their own printer drivers and methods for selecting a port as well.
On older systems, the parallel port is on an expansion card with the video adapter. These should
include a way to disable the video adapter, so you can use the parallel port in any system.
2.6 Port Hardware
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The parallel port’s hardware includes the back-panel connector and the circuits and cabling
between the connector and the system’s expansion bus. The PC’s microprocessor uses the
expansion bus’s data, address, and control lines to transfer information between the parallel port
and the CPU, memory, and other system components.
2.7 Connectors
The PC’s back panel has the connector for plugging in a cable to a printer or other device with a
parallel-port interface. Most parallel ports use the 25-contact D-sub connector shown in Figure
above. The shell (the enclosure that surrounds the contacts) is roughly in the shape of an uppercase D. Other names for this connector are the subminiature D, DB25, D-shell, or just D
connector. The IEEE 1284 standard for the parallel port calls it the IEEE 1284-A connector.
Newer parallel ports may use the new, compact, 36-contact IEEE 1284-C.
The connector on the computer is female, where the individual contacts are sockets, or
receptacles. The cable has a mating male connector, whose contacts are pins, or plugs.
The parallel-port connector is usually the only female 25-pin D-sub on the back panel, so there
should be little confusion with other connectors.
Some serial ports use a 25-contact D-sub, but with few exceptions, a 25-pin serial D-sub on a PC
is male, with the female connector on the cable—the reverse of the parallel-port convention.
(Other serial ports use 9-pin D-subs instead.)
SCSI is another interface whose connector might occasionally be confused with the parallel
port’s. The SCSI interface used by disk drives, scanners, and other devices usually has a 50contact connector, but some SCSI devices use a 25-contact D-sub that is identical to the parallelport’s connector.
If you’re unsure about which is the parallel-port connector, check your system documentation.
When all else fails, opening up the enclosure and tracing the cable from the connector to an
expansion board may offer clues.
2.8 Alternatives to the Parallel Port
The parallel port is just one of many ways to interface inputs and outputs to a computer. In spite
of its many virtues, the parallel port isn’t the best solution for every project. These are some of the
alternatives:
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Serial Interfaces
One large group of parallel-port alternatives is serial interfaces, where data bits travel on a single
wire or pair of wires (or in the case of wireless links, a single transmission path.) Both ends of the
link require hardware or software to translate between serial and parallel data. There are many
types of serial interfaces avail-able for PCs, ranging from the ubiquitous RS-232 port to the newer
RS-485, USB, IEEE-1394, and IrDA interfaces.
RS-232
Just about every PC has at least one RS-232 serial port. This interface is especially useful when
the PC and the circuits that you want to connect are physically far apart.
As a rule, parallel-port cables should be no longer than 10 to 15 feet, though the IEEE-1284
standard describes an improved interface and cable that can be 10 meters (33 feet). In contrast,
RS-232 links can be 80 feet or more, with the exact limit depending on the cable specifications
and the speed of data transfers.
RS-232 links are slow, however. Along with each byte, the transmitting device normally adds a
start and stop bit. Even at 115,200 bits per second, which is a typical maximum rate for a serial
port, the data-transfer rate with one start and stop bit per byte is just 11,520 bytes per second.
RS-485
Another useful serial interface is RS-485, which can use cables as long as 4000 feet and allows
up to 32 devices to connect to a single pair of wires. You can add an expansion card that
contains an RS-485 port, or add external circuits that convert an existing RS-232 interface to RS485. Other interfaces similar to RS-232 and RS-485 are RS-422 and RS-423.
Universal Serial Bus
A new option for I/O interfacing is the Universal Serial Bus (USB), a project of a group that
includes Intel and Microsoft. A single USB port can have up to 127 devices communicating at
either 1.5 Megabits/second or 12 Megabits/second over a 4-wire cable. The USB standard also
describes both the hardware interface and software protocols. Newer PCs may have a USB port
built-in, but because it’s so new, most existing computers can’t use it without added hardware and
software drivers.
IEEE 1284-1994 Standard
The recently released standard, "IEEE Std.1284-1994 Standard Signaling Method for a Bi-directional
Parallel Peripheral Interface for Personal Computers", is for the parallel port what the Pentium processor is
to the 286.
The standard provides for high speed bi-directional communication between the PC and an external
peripheral that can communicate 50 to 100 times faster than the original parallel port. It can do this and
still be fully backward compatible with all existing parallel port peripherals and printers.
The 1284 standard defines 5 modes of data transfer. Each mode provides a method of transferring data in
either the forward direction (PC to peripheral), reverse direction (peripheral to PC) or bi-directional data
transfer (half duplex). The defined modes are:
Forward direction only
Compatibility Mode: "Centronics" or standard mode
Reverse direction only
Nibble Mode: 4 bits at a time using status lines for data. Hewlett Packard Bi-tronics
Byte Mode: 8 bits at a time using data lines, sometimes referred to as a "bi-directional" port.
Bi-directional
EPP Enhanced Parallel Port- used primarily by non-printer peripherals, CD ROM, tape, hard
drive, network adapters, etc....
ECP Extended Capability Port- used primarily by new generation of printers and scanners
All parallel ports can implement a bi-directional link by using the Compatible and Nibble modes for data
transfer. Byte mode can be utilized by about 25% of the installed base of parallel ports. All three of these
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modes utilize software only to transfer the data. The driver has to write the data, check the handshake lines
(i.e.: BUSY), assert the appropriate control signals (i.e.: STROBE) and then go on to the next byte. This is
very software intensive and limits the effective data transfer rate to 50 to 100 Kbytes per second.
In addition to the previous 3 modes, EPP and ECP are being implemented on the latest I/O controllers by
most of the Super I/O chip manufacturers. These modes use hardware to assist in the data transfer. For
example, in EPP mode, a byte of data can be transferred to the peripheral by a simple OUT instruction.
The I/O controller handles all the handshaking and data transfer to the peripheral.
Overall, the 1284 standard provides the following:
1. 5 modes of operation for data transfer
2. A method for the host and peripheral to determine the supported modes and to negotiate to the
requested mode.
3.Defines the physical interface
Cables
Connectors
4.Defines the electrical interface
Drivers/Receivers
Termination
Impedance
In summary, the 1284 parallel port provides an easy to use, high performance interface for portable
products and printers.
IEEE 1284 History
When IBM introduced the PC, in 1981, the parallel printer port was included as an alternative to the slower
serial port as a means for driving the latest high performance dot matrix printers. The parallel port had the
capability to transfer 8 bits of data at time whereas the serial port transmitted one bit at a time. When the
PC was introduced, dot matrix printers were the main peripheral that used the parallel port. As technology
progressed and the need for greater external connectivity increased, the parallel port became the means by
which you could connect higher performance peripherals. These peripherals now range from printer sharing
devices, portable disk drives and tape backup to local area network adapters and CD ROM players.
The problems faced by developers and customers of these peripherals fall into three categories. First,
although the performance of the PC has increased dramatically, there has been virtually no change in the
parallel port performance or architecture. The maximum data transfer rate achievable with this architecture
is around 150 kilobytes per second and is extremely software intensive. Second, there is no standard for the
electrical interface. This causes many problems when attempting to guarantee operation across various
platforms. Finally, the lack of design standards forced a distance limitation of only 6 feet for external
cables.
In 1991 there was a meeting of printer manufacturers to start discussions on developing a new standard for
the intelligent control of printers over a network. These manufacturers, which included Lexmark, IBM,
Texas Instruments and others, formed the Network Printing Alliance. The NPA defined a set of parameters
that, when implemented in the printer and host, will allow for the complete control of printer applications
and jobs.
While this work was in progress it became apparent that to fully implement this standard would require a
high performance bi-directional connection to the PC. The usual means of connection, the ordinary PC
parallel port, did not have the capabilities required to meet the full requirements or abilities of this standard.
The NPA submitted a proposal to the IEEE for the creation of a committee to develop a new standard for a
high speed bi-directional parallel port for the PC. It was a requirement that this new standard would remain
fully compatible with the original parallel port software and peripherals, but would increase the data rate
capability to greater than 1M bytes per second, both in and out of the computer. This committee became the
IEEE 1284 committee.
The IEEE 1284 standard, "Standard Signaling Method for a Bi-directional Parallel Peripheral Interface for
Personal Computers", was approved for final release in March of 1994.
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IEEE 1394
The IEEE-1394 high-performance serial bus, also known as Firewire, is another new interface. It
allows up to 63 devices to connect to a PC, with transmission rates of up to 400 Megabits per
second. The 6-wire cables can be as long as 15 feet, with daisy chains extending to over 200
feet. The interface is especially popular for connecting digital audio and video devices. IEEE-1394
expansion cards are available for PCs.
IrDA
The IrDA (Infrared Data Association) interface allows wireless serial communications over
distances of 3 to 6 feet. The link transmits infrared energy at up to 115,200 bits/second. It’s
intended for convenient (no cables or connectors) transmitting of files between a desktop and
laptop computer, or any short-range communications where a cabled interface is inconvenient.
Some computers and peripherals now have IrDA interfaces built-in.
Other Parallel Interfaces
SCSI and IEEE-488 are two other parallel interfaces used by some PCs.
SCSI
SCSI (small computer system interface) is a parallel interface that allows up to seven devices to
connect to a PC along a single cable, with each device having a unique address. Many
computers use SCSI for interfacing to internal or external hard drives, tape back-ups, and CDROMs. SCSI interfaces are fast, and the cable can be as long as 19 feet (6 meters). But the
parallel-port interface is simpler, cheaper, and much more common.
IEEE 488
The IEEE-488 interface began as Hewlett Packard’s GPIB (general-purpose interface bus). It’s a
parallel interface that enables up to 15 devices to communicate at speeds of up to 1 Megabit per
second. This interface has long been popular for interfacing to lab instruments. Expansion cards
with IEEE-488 interfaces are available.
Custom I/O Cards
Many other types of input and output circuits are available on custom expansion cards. An
advantage of these is that you’re not limited by an existing interface design. The card may contain
just about any combination of analog and digital inputs and outputs. In addition, the card may
hold timing or clock circuits, function generators, relay drivers, filters, or just about any type of
component related to the external circuits. With the standard parallel port, you can add these
components externally, but a custom I/O card allows you to place them inside the computer.
To use an expansion card, you of course need an empty expansion slot, which isn’t available in
portable computers and some desktop systems. And the custom hardware requires custom
software.
PC Cards
Finally, instead of using the expansion bus, some I/O cards plug into a PC Card slot, which
accepts slim circuit cards about the size of a playing card. An earlier name for these was
PCMCIA cards, which stands for Personal Computer Memory Card International Association,
whose members developed the standard. Many portable computers and some desktop models
have PC-Card slots.
Popular uses include modems and data acquisition circuits. There are even PC Cards that
function as parallel ports. You don’t need an internal expansion slot, and you don’t have to open
up the computer to plug the card in. But again, the standard parallel-port interface is cheaper and
more widely available.
3. The Circuits Inside
Inside the computer, the parallel-port circuits may be on the motherboard or on a card that plugs
into the expansion bus.
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The motherboard is the main circuit board that holds the computer’s microprocessor chip as well
as other circuits and slots for expansion cards. Because just about all computers have a parallel
port, the port circuits are often right on the motherboard, freeing the expansion slot for other uses.
Notebook and laptop computers don’t have expansion slots, so the port circuits in these
computers must reside on the system’s main circuit board.
The port circuits connect to address, data, and control lines on the expansion bus, and these in
turn interface to the microprocessor and other system components.
The parallel port circuit does not contain an 8255 PPI.
IBM originally supplied three adapters that included a parallel printer port for its PC/XT/AT range
of microcomputers.
Depending on which were installed, each available parallel port's base address in the processor's
I/O space would be one of 278, 378 and 3BC (all Hex).
Most (All?) contemporary PCs, shipped with a single parallel printer port, seem to have the base
address at 378 Hex.
The PC parallel port adapter is specifically designed to attach printers with a parallel port
interface, but it can be used as a general input/output port for any device or application that
matches its input/output capabilities. It has 12 TTL-buffer output points, which are latched and
can be written and read under program control using the processor IN or OUT instruction. The
adapter also has five steady-state input points that may be read using the processor's IN
instruction.
In addition, one input can also be used to create a processor interrupt. This interrupt can be
enabled and disabled under program control. Reset from the power-on circuit is also ORed with a
program output point, allowing a device to receive a power-on reset when the processor in reset.
The input/output signals are made available at the back of the adapter through a right-angled,
PCB-mounted, 25-pin, D-type female connector. This connector protudes through the rear panel
of the system, where a cable may be attached.
When this adapter is used to attach a printer, data or printer commands are loaded into an 8-bit,
latched, output port, and the strobe line is activated, writing data to the printer. The program then
may read the input ports for printer status indicating when the next character can be written, or it
may use the interrupt line to indicate "not busy" to the software.
The Parallel Port Printer Adopter Block Diagram
Address
Decoder
Address Bus
Buffer
Control
Signals
Interrupt
Data Bus
Data
Buffer/
Latch for
Output
25 – PIN
D-Type
Connector
Control
Input
Buffer
Data
Wrap
Buffer
Control Wrap
and Signal Input
The output ports may also be read back at the card's interface for diagnostic loop functions. This
allows faults to be isolated between the adapter and the attached device.
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The original IBM-PC's Parallel Printer Port had a total of 12 digital outputs and 5 digital inputs
accessed via 3 consecutive 8-bit
ports in the processor's I/O space.
8 output pins accessed via the DATA Port
5 input pins (one inverted) accessed via the STATUS Port
4 output pins (three inverted) accessed via the CONTROL Port
The remaining 8 pins are grounded
4. Programming Considerations:
The printer adapter responds to five I/O instructions: two output and three input. The output
instructions transfer data into two latches whose outputs are presented on the pins of a 25-pin Dtype female connector.
Two of the three input instructions allow the processor to read back the contents of the two
latches. The third allows the processor to read the realtime status of a group of pins on the
connector.
A description of each instruction follows
Output to address 278/378/3BC Hex
Bit
Pin
7
9
6
8
5
7
4
6
3
5
2
4
1
3
0
2
The instruction captures data from the data bus and is present on the respective pins. These pins
are each capable of sourcing2.6 mA and sinking 24 mA. It is essential that the external device not
try to pull these lines to ground.
Output to address 27A/37A/3BE Hex
Bit
Pin
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7
-
6
-
5
-
4
IRQ
Enable
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~3
17
2
16
~1
14
~0
1
13
This instruction causes the latch to capture the least significant bits of the data bus. The four least
significant bits present their outputs, or inverted versions of their outputs, to the respective pins
shown above. If bit 4 is written as 1, the card will interrupt the processor on the condition that pin
10 transitions high to low.
These pins are driven by open collector drivers pulled to +5 Vdc through 4.7 k-ohm resistors.
They can each sink approximately 7 mA and maintain 0.8 volts down-level.
Input from address 278/378/3BC Hex
This command presents the processor with data present on the pins associated with the
corresponding output address. This should normally reflect the exact value that was last written. If
an external device should be driving data on these pins (in violation of usage groundrules) at the
time of an input, this data will be ORed with the latch contents.
Input from address 279/379/3BD Hex
This command presents realtime status to the processor from the pins as follows.
Bit
Pin
7
11
6
10
5
12
4
13
3
15
2
-
1
-
0
-
Input from address 27A/37A/3BE Hex
This instruction causes the data present on pins 1, 14, 16, 17 and the IRQ bit to be read by the
processor. In the absence of external drive applied to these pins, data read by the processor will
exactly match data last written to the corresponding output address in the same bit positions.
Note that data bits 0-2 are not included. If external drivers are dotted to these pins, that data will
be ORed with data applied to the pins by the output latch.
Bit
Pin
7
-
6
-
5
-
4
3
2
IRQ
~17 16
Enable
Note
0
1
0
Note: state assumed after processor reset:
1
~14
0
~1
1
1
4.1 Registers:
The following Tbale shows the register/port address available at the Printer Port. An X means
available.
7
6
5
4
3
2
1
0
I/O Port Address
Data
X
X
X
(D)
Status
~X
X
X
(S)
Control
(C)
Note: ~ are inverted signals
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X
X
X
X
~X
X
X
Hex 378
Hex 379
X
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~X
~X
Hex 37A
14
4.2 Interface with External Device
The interface of printer port with an external device is shown in the above diagram.
4.3 Signal Desciption
The following table shows the signal description.
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4.4 The Connector Pin Layout
IBM-PC Parallel Printer Port Female DB-25 Socket external Pin layout
______________________________________________________
/
\
\ 13 12 11 10
9
8
7
6
5
4
3
2
1 /
\
/
\
25 24 23 22 21 20 19 18 17 16 15 14
/
\__________________________________________________/
4.5 Software Considerations
QBasic
QBasic provides access to the I/O ports on the 80x86 CPU via the INP function and the OUT statement.
INP(portid) ' returns a byte read from the I/O port portid
OUT portid, value ' writes the byte value to the I/O port portid
portid can be any unsigned integer in the range 0-65535. value is in the range 0-255.
For example:
pdata = &H378
status = &H379
control = &H37A
OUT pdata, bits ' output data
bits = INP(status) ' input data
Turbo Pascal
Turbo Pascal provides access to the I/O ports on the 80x86 CPU via two predefined arrays, Port and
PortW.
var Port: array[0..65535] of byte;
PortW: array[0..65534] of word;
The indexed elements of each array match the port at the corresponding I/O address. Assigning a value to
an element of the Port or PortW arrays causes that value to be written out to the corresponding port. When
an element of the Port or PortW arrays is referenced in an expression, the value is read in from the
corresponding port.
Const Data = $378;
Status = Data + 1;
Control = Data + 2;
var Bits: Byte;
Port[Data] := Bits; { output data }
Bits := Port[Status]; { input data }
Turbo C and Borland C/C++
Turbo C and Borland C/C++ provide access to the I/O ports on the 80x86 CPU via the predefined functions
inportb / inport and outportb / outport.
int inportb(int portid);
/* returns a byte read from the I/O port portid */
int inport(int portid);
/* returns a word read from the I/O port portid */
void outportb(int portid, unsigned char value);
/* writes the byte value to the I/O port portid */
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void outport(int portid, int value);
/* writes the word value to the I/O port portid */
#include <stdio.h>
#include <dos.h>
#define Data 0x378
#define Status 0x379
#define Control 0x37a
unsigned char Bits;
outportb(Data,Bits); /* output data */
Bits = inportb(Status); /* input data */
Microsoft Visual C/C++
Microsoft Visual C/C++ provides access to the I/O ports on the 80x86 CPU via the predefined functions
_inp / _inpw and_outp / _outpw.
int _inp(unsigned portid);
/* returns a byte read from the I/O port portid */
unsigned _inpw(unsigned portid);
/* returns a word read from the I/O port portid */
int _outp(unsigned portid,
int value);
/* writes the byte value to the I/O port portid */
/* returns the data actually written
*/
unsigned _outpw(unsigned portid,
unsigned value);
/* writes the word value to the I/O port portid */
/* returns the data actually written
*/
portid can be any unsigned integer in the range 0-65535
#include <conio.h> /* required only for function declarations */
#define Data 0x378
#define Status 0x379
#define Control 0x37a
int Bits,
/* 0 <= Bits <= 255 */
Dummy;
Dummy = _outp(Data,Bits); /* output data */
Bits = _inp(Status);
/* input data */
Debug
Finally, of course, you can use the very old Debug.
Type the following command at C prompt to see the help for Debug.
C:\>debug /?
Runs Debug, a program testing and editing tool.
Debug [[drive:][path]filename [testfile-parameters]]
[drive:][path]filename Specifies the file you want to test.
testfile-parameters Specifies command-line information required by
the file you want to test.
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After Debug starts, type ? to display a list of debugging commands.
Debug provides input and output commands i port_address
o port_address byte_value
C:\>debug
-o 378 5a
-i 379
7F
-q
C:\>
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5 INPUT and OUTPUT Experiment.
5.2 The OUTPUT Experiment
Procedure: Experiment Output data using parallel. The shaded area on main block diagram shows the part
of the LUMS Parallel Port Interface Board (LPPIB) that is going to be used in this experiment. Connect the
connector as instructed by the TA. This will connect output port (378) to 8 LEDs on the side thorough
220 resistors as described in the diagram below:
Output
from 378
decoder
EN
8-bit
Output
Register/
Latch
Resistors
Parallel
Port
Connector
Data Bus
LEDs
2
3
4
LSB
8
MSB
25
Part of Computer I/O Card
5.2.1 Testing the circuit: Basic Output
Go into Debug.
Ask instructor if you are not sure how to.
Using the following debug command format:
O 378, <number between 0 – FF (hex)>
For example
O 378, FF
/* all LEDS ON */
O 378, 00
/* All LEDs OFF */
O 378, 20
O 378, ff
Output some data and by looking at the LEDs that are lit, confirm you experiment.
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Output Port
6 7 8 9
2 3 4 5
DB-25 Connector to
Computer Parallel Port
Input
Port
1, 14 (for
Row/
Coloumn
Select)
8 X 8 Matrix Display
Resistors
Row
Latch
Coloumn
Latch
Matrix Connector
LEDs
1,14 (O/P)
Kick
Start
Switch
LEDs
ADC
0804
LUMS Parallel Port Interface Board
DIP SWITCH
Connector
Analog to Digital
Connector
Analog
I/P
Power
Supply
Section
0-5 V
Analog
747 Dual
Op Amp
EN
MOTOR
Sensor
O/P
74244
as
MUX
+5
Analog
Output
From Variable Power Supply
Digital to Analog
Connector
5.2.2 Programming Assignments
These programming assignments will given in Turbo C by TA.
1. Lit all the alternate LEDs
2. Lit 4 MSB LEDs
3. Make them all ON/OFF using delay loop
4. Any assignment suggested by you
Project: The roulette wheel. A roulette wheel has circular number markings and a rotating pointer in the
center. Once the pointer is moved and assuming a fair pointer, it can stop at any number. This device is
usually used in “Qura Andazi”. Using a paper tape, mark all the eight LEDs and now program for roulette
wheel. This project will be further explained in the Class.
Questions:
1. How will you ensure your roulette wheel becomes platform independent?
2. How will you include true randomness in the roulette wheel?
5.3 The INPUT Experiment
Procedure
The Standard Parallel Port can only input 5-bit data. We will use 4-bits to perform Nibble Mode input of 8bit data. In part I of the experiment we will input only 4-bit and in part II we will use 74LS244 device to
input 8-bit data. The 4 nibbles will be ‘combined’ in the software to form an 8-bit byte.
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1,14 (O/P)
Output Port
9
8
7
6
5
4
3
1, 14 (for
Row/
Coloumn
Select)
2
DB-25 Connector to
Computer Parallel Port
Input
Port
8 X 8 Matrix Display
Resistors
Row
Latch
Coloumn
Latch
Matrix Connector
LEDs
5.3.1 Part I: Nibble Input
The following diagram shows the circuit that is going to be used in part I and II of this part of experiment
in shaded area and the shaded lines show where the connectors are to be connected.
Kick
Start
Switch
LEDs
ADC
0804
LUMS Parallel Port Interface Board
DIP SWITCH
Connector
Analog to Digital
Connector
Analog
I/P
Power
Supply
Section
0-5 V
Analog
747 Dual
Op Amp
EN
MOTOR
Sensor
O/P
74244
as
MUX
+5
Analog
Output
From Variable Power Supply
Digital to Analog
Connector
Connect the circuit for input port (4-bit only). (Ask your TA).
Use DIP switches to simulate input.
5.3.2
Study of Key Bounce and Debounce
Whenever the position of a mechanical switch is changed, it bounces many times before becoming stable
due to spring action. This can be problem for high speed reading of a key status using computer. Either
hardware or software methods can be adopted to eliminate the key bounce. In this experiment you will
study the key bounce and then write a software debouncing solution.
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5.3.3 Part II: Nibble Mode Input
In nibble mode input, two nibbles are read one at a time and the are combined to form a byte in software.
Basic Algorithm is:
1. Enable 74244 buffer to read the high nibble using Port 0378 (Outport (0x378, 00))
2. Read the high nibble from 379h.
3. Mask out the 4 required bit (MASK = 0x78)
4. Divide by 8 (shift right 3 in logic)
5. Save this in variable lnibble
6. Enable 74244 buffer to read the low nibble using Port 0378 (Outport (0x378, 0xFF))
7. Read the high nibble from 379h.
8. Multiply by 2 (Shift left one in logic)
9. Add this to hnibble to form the in_byte.
10. Repeat 1- 7 indefinitely if required.
The circuit diagram is given below.
Output from 0x0378
EN
4-bit
Input
Buffer
10
Parallel
Port
Connector
4
11
DIP Switches
Output
from 379
decoder
12
13
Data Bus
4
25
74 244
Tri-State
Buffers
Part of Computer I/O Card
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5.3.3
Programming Project: Printer Status Emulator
Through Printer Port, a printer sends the following signals:
Printer Off
Printer Offline
Paper out
Printer Ready (Idle)
Printer Busy
Printer Idle for Too Long
Assign one switch combination to one the above conditions of the printer, and then write a program that
will give printer status.
Your should submit a written report for all the programming assignments in this experiment on A4 size
papers.
Written report will be due next time you come for experiment.
State your assumption clearly.
All programs should be full of comments and variable names should be appropriate.
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