MC68HC11
System Overview
MC68HC11
System Overview
System block diagram (A8 version)
68HC11: major features
 HCMOS Technology (low power / high speed)
 On-chip RAM, ROM, EEPROM
 Basic core functions of MC6801 --improved
instruction set functionality
 2 operating modes and 2 test modes
 On-chip counter / timer
 On-chip analog-to-digital conversion
 On-chip parallel and serial ports
 Improved interrupt capabilities than earlier products
 supports 21 interrupt vectors
 Some fault detection capability for major errors
(power, illegal instruction, hung processor)
68HC11: major features
 Available in at least 25 different versions
– Different pin counts and packaging
– Different amounts/types of memory
» RAM size (192 to 1.25K bytes)
» ROM size (4K to 32K bytes)
» EEPROM (512 to 2K bytes)
» ROM, EPROM, or EEPROM program memory
Memory maps vary from version to version!
– Different I/O capabilities
(number of timers, chip selects, DMA channels,
A/D types, etc.)
CONTD
68HC11: major features
 Our textbook
generally discusses the
68HC11A8 version, but we use the 68HC11E9 in
the lab
– A8:
256 bytes RAM
8 KB ROM
512 bytes EEPROM
– E9:
512 bytes RAM
12 KB ROM
512 bytes EEPROM
68HC11: major features
Pin assignments
 Basic support pins
– Vdd, Vss: power (+5V) and ground
– Xtal, Extal: crystal connection for internal
oscillator
– E: "enable" clock output signal (input freq ÷ 4)
– Reset*: external reset; system failure indicator
– IRQ*, XIRQ*: interrupt request lines
– MODA, MODB: specifies operating mode
CONTD
Pin assignments
Port functions (in addition to parallel I/O)
– Port A: timer functions
– Port B: strobed outputs, expanded mode address
(high byte)
– Port C: parallel I/O, expanded mode address (low
byte) and data
– Port D: general serial I/O pins, handshake lines for
expanded mode
– Port E: A/D conversion
Modes of operation
 The
chip has
2 “operating” modes and
2 “test” modes
Mode determination:
– On reset or power up, the mode is selected by values on pins
MODA and MODB
» Jumpers J3 and J4 on EVBU trainer kit
– During operation, mode can be changed in some cases by
writing to the HPRIO register
2 “operating” modes
Single chip (MODA=0, MODB=1)
– No external address and data bus functions
» CPU can only access on-chip memory
– Ports B and C are general purpose parallel I/O
– All software needed to control MCU must be in internal
memory
– On reset, execution begins at address $E000
» Located in ROM
» For EVBU version, checks jumper J2, may jump to
CONTD
$B600 (EEPROM)
2 “operating” modes
 Expanded multiplexed (MODA=MODB=1)
– External memory and peripheral devices can be accessed
by time-multiplexed address-data bus
– Port B used for high byte of address (output)
– Port C provides low byte of address (output) and 8- bit
data (bi-directional)
– External address latch is required
– Execution begins at address $E000
» Just as in single-chip mode, jumper J2 can be used to
have the program jump to address $B600
2 “test” modes
Special bootstrap (MODA=MODB=0)
– On power up or reset, the program in the
bootstrap ROM is executed
– CPU waits for a 256-byte program segment to
be downloaded through the serial link and
stored starting at address $0000
– Execution then begins at address $0000
– Permits wide variety of programs to be
downloaded
CONTD
2 “test” modes
 Special test (MODA=1, MODB=0)
– Primarily a testing mode for the manufacturer
– Overrides some automatic protection
mechanisms -- risky!
On-chip memory
 ROM (12K bytes)
– Factory programmed
– Special bootstrap ROM
 RAM (512 bytes)
– Data, stack
– Can be used for downloaded code
– Low-power standby mode
 EEPROM (512 bytes)
– Programmed and erased on-chip
– Calibration storage, diagnostic log, critical data
logging, security data
CONTD
Off-chip memory
 EPROM
– For prototype development
– Windowed and one-time
programmable versions
Memory maps
 Different versions of the HC11 have
different memory maps: type,
quantity, and location of memory
varies
 Be sure to know which version you
are using!
– Our text references the generic HC11A8
version
– We use the HC11E9 version in the lab
Working with memory
 Usually work with 8-bit
data values in HC11
(sometimes 16-bit values)
 Addresses are 16 bits
 Example:
Working with memory
 Often show memory contents as follows:
$110 8E 01 FF BD 60 00 CE 8A C0 31 E2 42 29 90 01 FE
Addr
16 data values
16-bit data values are stored in consecutive
memory locations
– MSB = first location
– LSB = second location
– What is the 16-bit value stored at location $11A?
68HC11 register set
68HC11 register set
 68HC11 CPU registers
– Accumulators ACCA and ACCB used for computations
» 8-bit values
» For 16-bit computation, ACCA and ACCB may be
combined and accessed as ACCD
– Index registers IX and IY generally used to hold addresses
» 16-bit values
» Used as pointers to memory locations
» Some instructions use them for 16-bit computation, also
CONTD
68HC11 register set
– SP and PC
» Used by the CPU
» Not generally used by the programmer
 Programming model
– Register-register operations
– Register-memory operations
– Memory-only operations
– Indexed addressing
Condition code register
5 on-chip I/O ports
 Port A (8 bits)
– 1 bidirectional pin, 4 output pins, 3 input pins
– Also used for timer
 Port D (6 bits)
– 6 bidirectional pins (controlled by direction register)
– Also used for asynchronous (SCI) and synchronous
serial (SPI) I/O
 Port E (8 bits)
– 8 input pins
– Also used for A/D converter
CONTD
5 on-chip I/O ports
 Port B (8 bits)
– 8 output pins with optional handshaking
– Also used as address in expanded mode (replaced by PRU)
 Port C (8 bits)
– 8 bidirectional pins with optional handshaking and
wired-or mode
– Also used as data/address in expanded mode (replaced
by PRU)
I/O registers
 HC11 includes 64 I/O registers
– Each has a specific function
– Some are used for system configuration
– Others are used to interface with the
different
I/O subsystems
» Control
» Status
» Data
CONTD
I/O registers
 These
registers are accessed like memory
locations
– Addresses $1000 to $103F
– Programming Reference Guide and textbook both contain list
of I/O registers
 Eg., you write a value to a specific I/O port by
storing a value to the corresponding memory location
– The PORTA register is at address $1000
– The instruction STAA $1000 will write the value in ACCA to
Port A
Programming model -summary
 Use ACCA and ACCB for most operations
and computations
– 8-bit values
 Use ACCD and/or IX for 16-bit computations
 IX and IY usually used to hold addresses
– Pointers to memory locations
Perform I/O by reading/writing I/O registers
– Memory locations $1000-$103F
 There are also several addressing modes -----but
that's a topic for another day
MC68HC11 EVBU
Universal Evaluation
Board

Kit includes
– MC68HC11 board
– Development software (freeware assembler, PCbug11
monitor, Buffalo monitor)
– Documentation
 Compact, low-cost "universal" evaluation
board
– MC68HC11E9 or MC68HCX711E9
» 12K ROM or EPROM
CONTD
MC68HC11 EVBU
Universal Evaluation
Board
» 512 bytes EEPROM
» 512 bytes RAM
– 8 MHz crystal (2 MHz bus clock)
– RS232 interface (MC145407) with DB25
connector
– Reset switch (MC34064P)
– Wire-wrap area
Added for ECPE 4535 at Virginia Tech:
– Power supply
– Protoboard area
– IASM11 assembler and SIM11 simulator
Designing with the
MC68HC11
 Understand HC11 capabilities
– Microcontroller resources
– Standard components such as switches and displays
 Understand application domain
– Application requirements
– Appropriate algorithms
– Data and signal formats
CONTD
Designing with the
MC68HC11
 Structure the design
– Decompose functions and map to resources
– Define interfaces between functions and keep
them simple
– Specify memory and timing requirements for
each function
– Understand interactions for timing, interrupts,
data, etc.