1. Programming 68HC11

2. Steps in programming MPU
START
FETCH TO CODE
DECODE OP CODE
FETCH OPERAND
ADDRESS IF ANY
EXECUTE THE
INSTRUCTION

3. Programming Language machine
Machine Language
Hex Machine language B6 C3 00 BB E0 FF B7 C4 AA

4. $ indicate that the address is in hex
LDAA load accumulator A B6
STAA store accumulator A B7
ADDA add to accumulator A BB
SUBA subtract to accumulator A B0
WAI halt 3E
JMP jump 7E
BEQ branch if equal to zero 27

5. Jump branch instruction
Memory Address hex
Memory word hex
Mnemonic
Description
C100 48
ASLA
Shift A left 1 bit
C101 7E
JMP
JUMP to C15F for the next instruction
C102 C1
ADDRESS OF THE NEXT INSTRUCTION
C103 5F
C104
C105 …
C15F B7
STAA
STORE IN MEMORY LOCATION C300
C160 C3
ADDRESS OF THE LOCATION WHERE THE CONTENTS OF
A WILL B STORED
C161 00

6. Branch Equal to Zero (BEQ) instruction
Memory Address hex
Memory word hex
Mnemonic
Description
C200 BO
SUBA
Shift A left 1 bit
C201 C2
JUMP to C15F for the next instruction
C202 9B
ADDRESS OF THE NEXT INSTRUCTION
C203 27
BEQ
RESULT OF THE LAST OPERATION IS ZERO BRANCH TO C219
C204 14
IF NOT GO TO C205 OFSET = 1416
C205 … ?? ?
PC = C205
+ OFSET
C219 B7
STAA
STORE IN ADDRESS C127
C21A C1
C21B

7. Terms Offset determines MPU’s next instruction
C1, 00 address of operand X
C1, 01 address of operand Y
C1, 02 address where the contents of the accumulator A will be stored
C1, 5F address of next instruction
C3, 00 address of location where the contents of A will be stored

8. Assembly language source program
Memory address
Instruction mnemonic
Comments
C200
LDAA $D0FF
Get first the data word
C203
ADDA $D500
Add second data word
C206
STAA $D700
Store sum in memory

9. LDAA code
Source Code
Object Code B6 D0 FF
LDAA
$D0FF

10. Assembly process typical steps
The online assembler program is loaded into the computer’s internal RAM’s (unless it is already in ROM)
The programmer loads the assembly language source program into the computer’s RAM, either from the keyboard or an external memory unit (like when using ASCII code for the characters)

11. Continuation
The computer then is commanded to execute the one-line assembler program
The computer executes the one-line assembler program which converts source code instruction such as LDAA $D0FF into object code that I places into RAM
Once instruction is placed in RAM the program then can be stored in disk for later use

12. Continuation
The object program can now be executed since it is in the executable machine.

13. High level languages
BASIC
FORTRAN
TURBO C++

14. Flowchart no yes Start Initialize COUNT=7 Initialize RESULT=0
Read data byte
from sensor
Add to RESULT
Decrement COUNT
Is count =0 ? no
yes
Store result
in memory
stop

15. Problems
How many consecutive location does an 8 bit microcomputer store a 48 bit word?
Answer
48 bit / 8 bit
6 consecutive memory location

16. A certain 32 bit computer has the following instruction word format:
Op code
Operands address
8 bits
16 bits
How many different instructions can this instruction word specify?
How many different memory addresses can it specify?
What internal memory capacity would this computer
require to operate at full capacity?
Answer
a) 256 bits b) c)

17. During the LDAA instruction data are taken from__________ and transferred to ___________
Memory location
STAA