1. Microprocessors

2. Functions of 68HC11 Microprocessor
Providing tuning and control signal for all elements of microcomputer
Fetching instruction and data from memory
Transferring data from memory
Decoding instruction
Performing arithmetic and logic operations called for by instructions
Responding to I/O generated control signals such as reset and interrupt

3. 68 HC MPU 5 16 bit registers 2 8 bit accumulators
8 bit condition code registers
Control bus signals are expandable

4. Timing and control section
Control Bus signal
AS signal
E clock
Reset

5. Functions of reset
Fetches the content of ROM address FFFE and loads into PCH
Fetches the content of ROM address FFFF and load it into PC1 so that (PC) is now 2AC6
Begin fetching and executing instruction at address 2AC6

6. Microprocessor common function
Initialize MPU registers
Initialize I/O device control registers
Perform test on system RAM
Check status of I/O devices
Send messages to output devices

7. Instruction register
When the MPU fetches an instruction word from memory it sends to the IR

8. Program Counter (PC)
Contains in the memory address of the next instruction code that the MPU is to fetch.

9. Accumulator
Register that takes part in most of the operations performed by the ALU
It is also the register in which the result are being placed after most ALU operations
The source of the operand and destination of the result

10. Data Address Register Memory address register
Address latching register
Used when executing ADD instruction

11. General Purpose register
GPR the accumulators can perform the function of a general purpose register in many programming situations.

12. Common GPR instruction access codes
Load GP from memory [M] > [GP]
Store GP in memory [GP] > [M]
Transfer contents of one GP register to another GP register : [GP1] > [GP2]
Increment GP by 1: [GP +1 ] > [GP]
Decrement GP by 1: [GP-1] > [GP]

13. If [GP] not = 0 branch back to 2
This set [GP] = COUNT
Start 1
Load [GP] with value = COUNT
Fron the memory
Program Loop 2
Instruction Sequence to be
Executed a number of times
= COUNT 3
Decrement [GP]
[GP -1] > [GP]
If [GP] not = 0 branch back to 2 4
Is [GP] = 0?
Yes 5
If [GP] =0 go to the next instruction in sequence
Next portion of
program

14. Index register
68HC11 has two 16 bit index register (index register Y and index register X)
Similar to general purpose register
Its operation is called index addressing
It holds address base C for X and Y index register

15. Offset instruction illustration for register X
Address
Instruction code
Mnemonic
Description
C000 A6
LDAA $04,X
Load accumulator A from address [X]+04.
C001 04
Offset byte
Effective Address = offset + [X]
= 04 + C450
= C454

16. Y register instruction illustration
Address
Instruction code
Mnemonic
Description
C000 18
LDAA $04,Y
Load accumulator A A6
from address [Y]+04.
C001 04
Offset byte
Effective Address = offset + [Y]
= 04 + C450
= C454

17. Important process during the operation
Accumulator A and B are cleared to zero before any ADD operation occurs
Index register [X] is initially loaded with the number 2067
Accumulator B is initially loaded with 07 which the number of memory locations to be added. ACCB is being used to count down the number of times that blocks 5-8 are executed
Blocks 5-8 are executed a total of seven times before ACCB is decrement to 00 program goes to block 9 to store the final sum in memory location 2068
The ADD operation (block 5) are executed using data from different address each time starting with 2067 and ending with 2061.this means the data is now loaded to the accumulator

18. Start 1
Clear [ACCA] 2
Clear [ACCB] 3
Load [X] with Value 2067 4
Load [ACCB] with value 07
Add data stored at
address [X] +00 to [ACAA] 5
Decrement [X] 6 9 7
Decrement ACCB No 10
Store [ACCA] in
memory
location 2068
Is [ACCB]=0?
HALT 8

19. Condition Code register
Consist of individual bits
Each bits is called Flags
This is the 68HC11code register b7 b6 b5 b4 b3 b2 b1 b0 S X H I N Z V C

20. Condition Code functions
C – Carry flag reflects the carry status of arithmetic operation.
V – the overflow use to indicate overflow whenever signed numbers are being added or subtracted
Z – zero flag is automatically set to 1
N – negative used to indicate any sign result of any arithmetic data manipulation
I- interrupt mask flag is used to indicate effects on the IRQ
H – Half carry flag is change only by addition instruction
X – X interrupt mask used to indicate not XIRQ
S – stop disable flag is used to prevent the stop instruction

21. Conditional branching
It examine the value of the zero flag
If zero flag is = 0
The next instruction will be taken at a normal sequence
If zero flag is = 1
The program will branch into new address for the next instruction
If carry clear (BCC) or set booth will examine the carry flag

27. Two operands operators
Add
Subtract

28. Accumulator and memory
instructions

29. Load, Store and transfer instruction

30. Arithmetic operation instruction

31. Continuation..

32. Multiply and divide instruction

33. Logical operation instruction

34. Shift and rotate instructions

35. Stack and index register instruction

36. Condition code register instruction

38. Branch instructions