Notes for January 19, 2001

68HC12 Address Space

68HC12 Address Space



RAM: Random Access Memory (can read and write)
ROM: Read Only Memory (programmed at factory)
PROM: Programmable Read Only Memory
(Program once at site)
EPROM: Erasable Programmable Read Only Memory
(Program at site, can erase using UV light and reprogram)
EEPROM: Electrically Erasable Programmable Read Only Memory
(Program and erase using voltage rather than UV light)

68HC12 has: 1 K RAM
768 bytes EEPROM
Can erase and reprogram any byte using normal 5V power supply
32 KB Flash EEPROM
Can erase using external 12V power supply

68HC12 Address Space


68HC12 ALU


When the control unit sees the sixteen-bit number 0x1806, it tells the ALU to add B to A, and store the result into A.

68HC12 Programming Model


68HC12 Programming Model


Some HC12 Instructions Needed for Lab 1

LDAA address Put the byte contained in memory at address into A
STAA address Put the byte contained in A into memory at address
CLRA Clear A (0 -> A)
INCA Add 1 to A ((A) + 1 -> A)
ABA Add B to A, store the result in A
ASRA Shift A right by one bit (keep the MSB the same)
This divides a signed number by 2
LSRA Shift A right by one bit (put 0 into MSB)
This divides an unsigned number by 2
NEGA Negate A (-(A) -> A)
TAB Transfer A to B ((A) -> B)
SWI Software Interrupt (Used to end all our HC12 programs)

A Simple HC12 Program

A Simple Assembly Language Program.

Assembling an Assembly Language Program

Bill Rison