INTRODUCTION TO 8096 MICROCONTROLLERS
SALIENT FEATURES :
INTEL 8096, a second generation processor belongs to MCS 96 family. This is a high
performance 16 bit microcontroller with register to register architecture. This is designed to
handle high speed calculations and fast input/output operations which is preferred in high speed
modern control applications. The 8096 with 16-bit CPU horse power, high speed math
processing and high speed I/O is ideal for complex motor control and axis control systems.
Hence it is used in 3 phase large horse power AC motors and robotics The 10-bit ADC option
makes it most suitable candidate for data acquisition systems and closed loop analog controllers.
8096 can be configured in two modes. ( i ) Single chip mode and (ii) Expanded mode. In
the single chip mode the internal ROM or EPROM is accessed by making the pin EA (Active
low) HIGH. For ROM less chip to access the external memory the pin EA is made low. In the
expanded mode both internal and external (OFF CHIP) memory can be accessed using the
multiplexed bus architecture. It has nearly 230 bytes of on-chip RAM and one 10-bit A/D
converter with sample hold circuit. There are five on chip I/O ports each of 8-bit width The 8096
bit microcontroller has a complete set of 16-bit arithmetic instructions including multiply and
divide operations. It has Pulse Width Modulation Output with dedicated Baud Rate Generator It
has one on chip Full Duplex Serial Port There are 20 interrupt sources and 8 interrupt vectors on
8096. It has two 16-bit Timers Timer 1 and Timer 2 and one 16 bit watch dog timer This 8096 is
available as 48 pin DIP(Dual In-line Package) and 68 pin PLCC and also 68 pin leadless chip
carrier IC. It is also available as a 68 pin PGA(Pin Grid Array) package .
ARCHITECTURE :
8096 is a 16-bit microcontroller in which the data path for operands is 16 bits wide i.e when data
is transferred between RAM or ROM and the CPU, it is transferred 16 bits per internal memory
cycle. The 8096 has an internal 8-bit address bus and can access 2 8 addresses.The 8096 performs
most of the calculations in RALU. The RALU contains A 17 bit ALU One 16 bit program status
word (PSW) One program counter(PC) A loop counter and 3 temporary registers. All registers
are 16 bit or 17 bit wide. A separate incrementor is used for the Program Counter .
PSW Register :
PSW Register IS A 16 bit Register, whose lower byte can act as INT_MASK register . Z is the
zero flag N is the negative flag V is the overflow flag VT is the overflow Trap flag C is the carry
flag I is the global interrupt enable flag ST is the sticky bit, it is set during a right shift
Two of the temporary registers have their own shift logic. The addressable memory space on the 8096
is 64 kB , most of which are available to the user for program or data memory .The locations which have
special purpose are 0000H through 00FFH and 1FFFH through 2010H.All other locations can be used
either for program or for data storage or for memory mapped peripherals.
Memory Mapping: The 64kB memory space mapping is shown in the diagram
Fig.1 Memory Mapping
The 8096 has been designed for high speed /high performance control applications. Because the
8096 architecture is different from that of the 8048 or 8051 The architecture of 8096 has two
major sections one is the CPU section and the other is the I/O section.The block diagram is
shown in the figure 2
Fig.2.Block diagram of 8096 Microcontroller
CPU OF 8096:
The 8096 CPU has a 16-bit ALU which operates on a 256-byte register file instead of an
accumulator. Any of the locations in the register file can be used for sources or destinations for
most of the instructions. Hence this is called a register to register architecture. Many of the
instructions can also use bytes or words from anywhere in the 64K byte address space as
operands. Locations 00h through 17H are the I/O control registers or special function
registers(SFRs) Locations 18H and 19H contain the stack pointer which serves as general
purpose RAM when not performing the stack operations. The remaining bytes of the register file
serves as general purpose RAM ,accessible as bytes,words or double-words. Calculations
performed by the CPU takes place in the RALU .This RALU contains a 17 bit ALU ,the program
status word (PSW),the program Counter(PC),a loop counter and three temporary registers. The
RALU operates directly on the register files, thus eliminating the problem with Accumulator and
providing direct control of I/O operations through the SFRs.
I/O FEATURES :
Most of the I/O features on the 8096 are designed to operate with little CPU intervention. The
Watchdog Timer is an internal timer which can be used to reset the system if the software fails to
operate properly. The Pulse-Width-Modulation (PWM) output can be used as a rough D to A, a
motor driver, or for many other purposes. . The A to D converter (ADC) has 8 multiplexed inputs
and 10-bit resolution. The serial port has several modes and its own baud rate generator. The
High Speed I/O section includes a 16-bit timer, a 16-bit counter, a 4-input programmable edge
detector, 4 software timers, and a 6-output programmable event generator
PWM OUTPUT:
Analog outputs are just as important as analog inputs when connecting to a peripheral device.
True digital to analog converters are difficult to make on a microcontroller because of all of the
digital noise and the necessity of providing an on chip, relatively high current, rail to rail driver.
They also take up a fair amount of silicon area which can be better used for other features. The A
to D converter does use a D to A, but the currents involved are very small. The PWM signal is a
variable duty cycle, fixed frequency waveform that can be integrated to provide an
approximation to an analog output. The frequency is fixed at a period of 64 microseconds for a
12 MHz clock speed. Controlling the PWM simply requires writing the desired duty cycle value
(an 8-bit value) to the PWM Register.
General Purpose I/O PORTS :
There are five 8-bit I/O Ports namely Port 0, Port 1, Port 2, Port 3 and Port 4 .
PORT 0
Port 0 is only an Input port which is also used as the analog input port for the on chip ADC. So,
if the analog input features are not used ,the Port 0 Can be used as input port only .Port 0 is
shown in Fig 3
PORT 1:
This is a quasi bidirectional port which can be used either as input or as the out port. It is
mapped It is mapped at the memory address 0FH. If any of the port 1 pin is to be used as input
port the corresponding pin must be made high by writing the data 1. The weak internal pullup is
designed to be overridden by the external device which drives the line. When the output drive
capability is sufficient to drive a 74LSxx Input a CMOS device driven by port1 will require a
pullup resistor of around 10K to +5V in order to bring the output up well above the normal
CMOS threshold voltage of 2.5 volts.Port1 inputs can be driven by either CMOS or TTL devices
with no extra parts. Port 1 is shown in Fig 4 .
,
Fig 3 . PORT 0
Fig 4.Port 1
PORT 2:
The Port 2 has four input lines, two output lines andtwoquasi bidirectional I/O lines as shown in the Fig.
One or more of these six lines can be used f or alternate purpose of PWM ,RXD,TXD, Timer 2 Inputs etc..
PORT3 & PORT 4:
The Port3 & Port4 are similar in use.Both of them have open drain outputs. By writing 1 to any
line it can be used as an input and other lines can serve as output lines. Each output line require a
pullup resistor of about 15K.In the expansion mode ,the bus lines can gain the ability to drive
both high and low ,forming the expansion bus without the need of pullup resistors.
RESETS AND SELFPROTECTION OPTIONS:
RESETS AND SELFPROTECTION OPTIONS When the reset pin is driven to low the 8096,
regardless of what it is doing will reset and start executing from the address 2080H.The reset pin
is a bidirectional line with a strong internal pullup.T his line may also be driven by internal
watchdog timer also.The INTEL 8096 microcontroller is provided with on chip self protection
circuitary , to protect the chip from large currents. The chip is automatically reset when the Vdd
deviates from the prescribed levels. Diode circuits are provided on the chip itself ,which gives
self protection.
HIGH SPEED INPUT UNIT:
HIGH SPEED INPUT UNIT This unit is used to record the time at which an external event
occurs with respect to timer 1. It can monitor four independently configurable HSI lines and
capture the value of Timer 1 when an event takes place. There are 4 lines (HIS.0-HIS.3)available
in this unit .The HIS unit can store upto 8 entries(Timer 1 values) . The HSI unit can generate an
interrupt when loading an entry into the HIS holding register or loading the sixth entry into the
FIFO. The four types of events that can trigger captures include “rising edges only”, ”falling
edges only”,”rising or falling edges” or every eighth rising edge.
HIGH SPEED OUTPUT UNIT:
This HSO unit is used to trigger events at specified times based on Timer 1 or Timer 2 with
minimal CPU over-head. The 4 events are Starting an A/D conversion Resetting of Timer2
Setting four software flags Switching six output lines (HSO.0-HSO.5). The HSO unit stores
pending events and the specified time s in a Content Addressable Memory(CAM) file. This
CAM file stores up to 8 commands. Each command specifies the action time,the nature of the
action ,whether an interrupt is to occur and whether Timer 1 or Timer 2 is the reference Timer.
For every 8 state times the HSO compares the CAM locations for the time matches. The HSO unit
can generate two types of interrupts ( i ) HSO execution interrupt (Vector = 2006H) (ii) Software Timer
interrupt(Vector =200BH )
TIMERS:
INTEL 8096 controller has two on chip 16-bit timers TIMER 1 & TIMER 2 TIMER 1 can act as
a 16-bit counter also and can be clocked at every 2 ms. i.e for every 8-internal clock cycles. This
Timer is used in conjunction with high speed I/O system. When Timer 1 is over flown ,the
interrupt bit is enabled or disabled .. TIMER 2 can be used as a 16-bit even counter which is
clocked by a signal coming into the chip on either of the two pinsPort2.3 or HIS.1 The choice
between the two clock sources is made by setting or clearing bit 7 of the IOC.0 Timer 2 is
counted on both the rising edges and falling edges of the input signal and the minimum time
between edges is 2 micro seconds.
WATCH DOG TIMER:
An on chip 16-bit watch dog timer is available in 8096 which helps to recover the controller
from the software upsets. This 16-bit WDT is a counter which is incremented every state time.
This counter is cleared by program after periodic interval and not allowed to overflow . However
, if the program does not progress properly by any reason such as Electrostatic Discharge(ESD) or due
to any hardware related problems ,the overflow occurs. And the hardware reset is initiated to
restart the microcontroller. This process avoids the system from having a malfunction for longer
than 16mS under 12MHz frequency operation When the WDT overflows ,it pulls down the
RESET pin for at least two state times resetting 8096 and also any other devices connected to the
RESET line.
INTERRUPT STRUCTURE:
There are 20 different interrupt sources that can be used on the 8096. The 20 sources vector
through 8 locations or interrupt vectors. All these interrupts are enabled or disabled using the 9 th
bit of PSW register. If this bit is set to 1 all the interrupts are enabled and disabled when reset to
zero.Control of the interrupts is handled through the Interrupt Pending Register
(INT_PENDING), the Interrupt Mask Register (INT_MASK), and the I bit in the PSW (PSW.9).
The content of the interrupt mask register determine whether the pending interrupt is serviced or
not. If it is to be serviced , the CPU pushes the contents of the program counter on to the stack
and reloads it with the vector corresponding to the desired interrupt. When the hardware detects
one of the 8 interrupts , it sets the corresponding bit in the interrupt pending register .This
register can be read or modified as a byte register. Individual interrupts can be enabled or
disabled by setting or clearing the bits in the Interrupt mask register. The INT_MASK register
can be accessed as the lower bits of the PSW register.
SERIAL PORT:
The 8096 has an on-chip full duplex serial port to reduce the total number of chips required in
the system.The serial port is similar to that on the 8051 controller. . It has one synchronous and
three asynchronous modes. In the asynchronous modes baud rates of up to 187.5 K baud can be
used, while in the synchronous mode rates up to 1.5 M baud are available. The chip has a baud
rate generator which is independent of Timer 1 and Timer 2, so using the serial port does not
take away any of the HSI, HSO or timer flexibility or functionality. Control of the serial port is
provided through the SPCON/SPSTAT (Serial Port CONtrol /Serial Port STATus ) register. The
serial port is configured in four modes. The four modes of the serial port are referred to as modes
0, 1, 2 and 3. Mode 0 is the synchronous mode, and is commonly used to interface to shift
registers for I/O expansion. In this mode the port outputs a pulse train on the TXD pin and either
transmits or receives data on the RXD pin. Mode 1 is the standard asynchronous mode, 8 bits
plus a stop and start bit are sent or received.. Modes 2 and 3 handle 9 bits plus a stop and start
bit. The difference between the two is, that in Mode 2 the serial port interrupt will not be
activated unless the ninth data bit is a one; in Mode 3 the interrupt is activated whenever a byte is
received. These two modes are commonly used for interprocessor communication. Baud rates
for all of the modes are controlled through the Baud Rate register. This is a byte wide register
which is loaded sequentially with two bytes, and internally stores the value as a word. The least
significant byte is loaded to the register followed by the most significant. The most significant bit
of the baud value determines the clock source for the baud rate generator. Ifthe bit is a one, the
XTAL1 pin is used as the source, if it is a zero, the T2 CLK pin is used .
ADDRESSING MODES:
The 8096 instruction set supports six addressing modes. They are
Immediate addressing mode
Register direct addressing mode
Indirect addressing mode
Indirect with auto increment mode
Short indexed mode and
Long indexed mode.
These addressing modes increase the flexibility and overall execution speed of 8096 controller.
Each instruction uses at least one of the addressing modes. The register , direct and immediate
addressing modes execute faster than the other addressing modes. Both of the indirect addressing
modes use the value in a word register as the address of the operand. The indirect auto increment
mode, increments a word address by one after a byte operation and two after a word operation.
A to D CONVERTER:
Analog inputs are frequently required in every microcontroller application. The 8096 controller
has one 10 bit on chip A/D converter that can use any one of eight input channels. The
conversions are done using the successive approximation method, and require 168 state times (42
microseconds with a 12 MHz clock.). The main components of the A/D converter are 8-analog
input channels One 8 to 1 multiplexer. A sample and hold capacitor and Resistor ladder The A/D
converter performs a conversion in 88 time states .Upon the completion of each conversion the
converter can generate a conversion complete interrupt.
REFERENCES:
1. Design with Microcontrollers –John . B. Peatman – Mc.Graw -Hill International Ed.
2. Intel Application note & data sheet .