Microprocessor Dr. Rabie A. Ramadan Al-Azhar University Lecture 7

Z80 Assembly Programming 2

Programming Phases 3 High-level language (C, C++, Pascal) Assembly language (Z80) Machine language assembler compiler linker Object code

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 load B into A  LD  01, 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  (6H) byte (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 byte 1 LD BC (01H) byte 2 80H 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 (00H)  byte (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 Verify the value of a bit (0 or 1) Z flag is the indicator BIT 7, B  check bit 7 in register B Bit Set/Reset 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 A byte following the opcode is the operand LD B, 97H  97h id the value Immediate Extended Two bytes following the opcode are the operands LD BC, 3040H  3040H are the 2 bytes value Register 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 ( ) will be incremented 30

Addressing Modes Bit Used with bit operations SET 7, B Page zero 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. AddressHex codeOpcodeOperand 20003ELDA,97H LDHL, 2050H DDLDIX, 2075H LDC,A 200A44LDB,H 200B76HALT 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

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 LD A, 00H LD BC, 8058H LD B, A LD HL, 2040H LD L,C LD (HL), A HALT 43

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