Download Z80 Programming - Rabie A. Ramadan

Microprocessor
Dr. Rabie A. Ramadan
Al-Azhar University
Lecture 7
Z80 Assembly Programming
2
Programming Phases
High-level language
(C, C++, Pascal)
compiler
Assembly language (Z80)
assembler
Object code
linker
Machine language
3
Z80 Instruction Set

First, You are required to look for Z80
assembler to try some of the programs.

Z80 Includes all 8080 instructions

Contains 158 instructions

Instruction  Opcode + Operands
4
Instruction Format

Z80 instruction  ranges from one byte to four bytes

Opcode varies from 1 to 2 bytes

Operands varies from 1 to 2 bytes

Operands could be memory locations , registers, I/O
addresses , or memory addresses
5
Z80 instruction Set

Instructions can be classified to:
• 1-Byte instructions
• 2-Byte instructions
• 3-Byte instructions
• 4-Byte instructions
6
Z80 Instruction Set

1-Byte Instruction
• The opcode and operands are included in the same
byte
• Ex.
• LD A,B
• LD  01
load B into A  01 111 000
, A 1111 , and B 000
• For microprocessor internal usage only
7
Z80 Instruction Set

2-Byte Instructions
• Opcode  First Byte
• Operand  Second Byte
• Ex.
•
LD B, 32H  0000 0110 (6H) byte 1
0011 0010 (32H) byte 2
Load the “32” value into register B
LD B is represented by 6H and the second byte
includes “32”
8
Z80 Instruction Set

3-Byte Instruction
• One byte Opcode and two bytes Operand
• Ex. LD BC, 2080H
• 0000 0001 byte 1 LD BC (01H)
• 1000 0000 byte 2 80H
• 0010 0000 byte 3 20H
• Loads the value “2080H” into the two registers B and
•
C
Note: the load starts by the low order byte followed by
the high order  80 then 20
9
Z80 Instruction Set

4-Byte Instructions
• Not compatible with 8080 instruction set
• 2 bytes Opcode and 2 bytes Operand
• Ex.
LD IX , 2000H
• Loads the contents of memory address 2000H into IX register
first 2 bytes
• 0000 0000
• 0010 0000
(00H)  byte 3
(20H)  byte 4
10

Z80 Instruction Set

Instruction Categories
• Data Copy  transfer or load operations
• Arithmetic Operations
• Logic Operations
• Bit Manipulation
• Branch Operation
• Machine Control Operations
11
Data Copy Instructions




From register to register
• LD A, B  load B into A
Specific 8 bits data into register
• LD B, 32H  load “32” into B
Specific 16 bits data into register
• LD HL , 2080H  loads “2080” into HL
From memory location into register
• LD A , (2010H)  load the content of memory
location (2010) into A
12
Data Copy Instructions




From input port into accumulator
• IN A, (01H)  loads data from Input port (01H) into
A
From the accumulator into the o/p port
• OUT (07H) , A
Copy the contents of register into stack memory
• PUSH BC  pushes the BC contents into the stack
Exchange data between registers
• EXX BC, DE
13
Arithmetic Instructions

Addition
• Any thing is only added to the contents of the
•
•
•
accumulator.
No two registers such as B and C can be added
directly.
ADD A, B  add B to the accumulator contents
ADD A, 97H  add the value “97H” to the
accumulator content
14
Arithmetic Instructions

Subtraction
• A register or memory location can be subtracted from
•
•

the accumulator
SUB C  subtract the contents of register C from the
accumulator
SUB 47H  subtract the “47H” from the accumulator
Note : the accumulator in implied in the instruction
15
Arithmetic Instructions

Increment / Decrement
• Add / Sub1 to/from the contents of any register or
memory location
• INC B
• DEC BC
16
Arithmetic Instructions

1’s and 2’s Complement
• Do 1’s or 2’s complement on the contents of the
accumulator
• CPL
 one’s complement  changes the 1 to 0
and vice versa
• NEG
 2’s complement (subtract the
accumulator from 0 ) or (Add 1 to the 1’s
complement )
17
Group Activity

Write a simple program to load the values
“53H” and “F5H” into registers A and B
respectively. Then add the two registers?

LD A, 53H
LD B, F5H
ADD A, B


18
Logic Operations



Logic Functions
• AND , OR , XOR with the accumulator contents
• AND B
Shift and Rotate
• RLC B  rotate left the contents of B
Compare
• Compare the contents of a register with the contents of
a register or memory location  O/p will be shown on
the flag register
• CP B
19
Bit Manipulation

Bit Test

Bit Set/Reset
• Verify the value of a bit (0 or 1)
• Z flag is the indicator
• BIT 7, B  check bit 7 in register B
• SET 5, B
• RES 2, B
20
Branching Operations



Jump
• Change the program sequence
• JP C, 2050H  if C flag is set , jump to 2050H
Call/Return
• Change the program sequence by calling or returning from a
sub routine
• CALL 2050H  call subroutine located at 2050H
Restart
• Memory are divided into pages
• Page number 00 marked with 8 restart locations
• RST 28H  restart from the location 28H
21
Machine Control Operations

Control the Z80 operations

HALT  Suspend execution of an
instruction
22
How to write a program ?

Phases
• Problem Statement
• Analysis
• Flowchart
• Write the Assembly
• Execute
23
Flowchart Components
24
Write the Assembly

Will try to get our hands dirty in the lab
25
Addressing Modes

A way of specifying the operand or pointing to a data location
• Immediate
• Immediate extended
• Register
• Implied
• Register indirect
• Extended
• Relative
• Indexed
• Bit
• Page Zero
26
Implied Memory Addressing

Registers H and L hold the address of the memory location being
accessed
• LD C, (HL)  loads C register with the contents of the memory
location pointed by HL registers
27
Addressing Modes

Immediate

Immediate Extended

Register
• A byte following the opcode is the operand
• LD B, 97H  97h id the value
• Two bytes following the opcode are the operands
• LD BC , 3040H  3040H are the 2 bytes value
• Operand is a register
• LD A, B  B is a register
28
Addressing Modes



Implied
•
•
The opcode imply one of the operands
AND B  AND implies that the operation is done on the
accumulator contents
Register Indirect
•
•
Register holds the memory location address
LD B, (HL)  the memory location is stored in H and L registers
Extended
•
•
The two bytes following the opcode specify the jump location
JP 208H
29
Addressing Modes


Relative
• The oprand indicates the placement of the next
instruction to be executed relative to the current one
• JR 14H  from the next instruction , jump 20 locations
Indexed
• Use one of the index registers to define the next
instruction location
• INC (IX+10H)  if IX contains 2080H , then the
content of the memory location (2080 +10) will be
incremented
30
Addressing Modes

Bit

Page zero
• Used with bit operations
• SET 7, B
• Reset operation
• RST 28H
31
Reading Materials

Chapters 6 and 7

Please find one of the free Z80 assemblers
and play with it
32
Data Copy Operations
33
Load Instruction




LD rd , rs  copy data from rs to rd
LD r, 8-bit  immediate addressing mode , loaf 8 bit
number into register r
• LD B, 32H
LD rp , 16- bit  immediate extended addressing mode , load
16-bits into register pair
• LD HL, 1840H
LD rx, 16-bit  immediate extended addressing mode , loads
16 bits into specified index register
•
LD IX, 2050H
34
Load instructions
Example

Write a program to do the following:
• Load 97h into the accumulator
• Loads 2050H into HL register
• Loads 2070H into IX register
• Copy the contents of the accumulator into register C
• Copy the contents of register H into register B
• End the instructions by HALT
• Write all of these instructions at the memory locations
started at 2000H
• Show the register contents by the end of this program ?
35
Answer
Mem. Address
Hex code
Opcode
Operand
2000
3E
LD
A,97H
2001
97
2002
21
LD
HL, 2050H
2003
50
2004
20
2005
DD
LD
IX, 2075H
2006
21
2007
75
2008
20
2009
79
LD
C,A
200A
44
LD
B,H
200B
76
HALT
36
Data Copy Between Registers
and Memory




Memory Address stored in 16 bits
LD r, (HL)  Indirect Addressing mode , loads the contents of
a memory location whose address is stored in HL register pair
• LD , B, (HL)
LD (HR), r  Indirect Addressing mode , loads the contents
of a register into a memory location whose address is stored in
HL register pair
• LD (HL) , C
LD (HL), 8-bit  indirect and immediate , copy 8-bit into a
memory location whose address is stored in HL register pair.
• LD (HL), 97H
37
Data Copy Between Registers
and Memory


LD A, (rp)  indirect , copy the contents of a memory into A
LD (rp) , A  indirect , copy the contents of A into a memory
location
• LD (BC), A

LD A, (16-bit)  Extended , copy contents of memory into
accumulator

LD (16-bit), A  Extended , copy contents of the
accumulator into memory
• LD (2050H), A
38
Data Copy Between Registers and Memory
Example

The memory location 2050H contains the
data byte 37H , write instructions to copy a
byte from the memory location into register
B?
39
Answer

Method 1:
• LD HL, 2050H
• LD B, (HL)

Method 2:
• LD DE, 2050H
• LD A, (DE)
• LD B, A

Method 3:
• LD A, (2050H)
• LD B,A
40
Data Copy Between
Accumulator and I/O

IN A, (8-bit) read data from input port
to the accumulator

OUT (8-bit) , A  write data into the output
port

See Example in Page 191
41
Group Activity

Write comments to explain the function of
the following instructions
• LD HL, 2065H
• LD (HL), 00H
• HALT
42
Group Activity










Specify the contents of the registers and memory locations if
any after the execution of the following instructions:
A B C H L
34 7F FF 01 00
LD A, 00H
LD BC, 8058H
LD B, A
LD HL, 2040H
LD L,C
LD (HL), A
HALT
43


Useful Links are now available on the
website
http://www.diylife.com/2008/02/15/program-a-pic-microcontroller/


http://www.promeganet.com/?p=3


http://www.promeganet.com/?page_id=233


http://www.arabteam2000-forum.com/index.php?showtopic=76314
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