Microprocessor

Dr. Rabie A. RamadanAl-Azhar University

Lecture 8

Z80 Assembly Programming

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Arithmetic Operations

Addition and Subtraction Increment/Decrement 1’s and 2’s Complement

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Addition and Subtraction Performed in relation to the contents of the operands .

ADD A, r Add the contents of register r to the contents of the accumulator and stores the result back in the accumulator . Needs only one byte.

ADD A, 8-bit Add 8-bit data directly to the accumulator (2 bytes).

ADD A, (HL) Add memory contents to the accumulator (1 byte)

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Addition and Subtraction

SUB r subtracts the contents of register r from the accumulator.

SUB 8-bit subtract 8-bit from the accumulator

SUB (HL) subtract memory contents from the accumulator

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Increment/Decrement Instructions

INC/DEC r increment/ Decrement the contents of register r.

INC/DEC (HL) Increment/decrement the contents of memory

INC/DEC rp Increment/ decrement register pair (HL, DE, BC, SP)

One byte each

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1’s and 2’s Complement Instructions

Performs the complement on the accumulator contents .

CPL 1’s complement or inverts the contents of the accumulator (1 byte)

NEG 2’s complement. Subtracts the accumulator from 00 (2 bytes)

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Branch Operations

Jump instructions

Call and return instructions

Restart instructions

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Jump Instructions

Absolute Jump• Operands specifies the 16-bit address to which the

program sequence should be transferred

• Three bytes instruction

Relative Jump • Contains 8-bit displacement

• 2-byte instruction

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Absolute Jump

Unconditional Conditional

• Implemented based on the following flags • S sign

• Z Zero

• CY Carry

• P/V Parity/overflow

• Two instructions are associated with each flag. One when the flag is set and one when the flag is reset

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Absolute Jump JP 16-bit Jump unconditional to memory location

specified by the 16-bit operand

JP C, 16-bit Jump on carry to 16-bit address (CY=1)

JP NC, 16-bit Jump on no carry to 16-bit address (CY=0)

JP Z, 16-bit Jump on zero to 16-bit address (z = 1)

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Absolute Jump

JP NZ, 16-bit jump on zero to 16-bit address (Z = 0) JP M, 16-bit jump on minus to 16-bit address (S = 1) JP P, 16-bit Jump on positive to 16-bit address (S=0) JP PE, 16-bit Jump on parity even to 16-bit address

(P/V = 1) JP PO, 16-bit Jump on parity odd to 16-bit address

(P/V = 0)

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Relative Jump Instructions

Unconditional and Conditional types The instruction followed by 8-bit

displacement/offset value Offset could be positive (forward) (D6-D0

and MSB is always 0) Offset could be negative (backward) (2’s

complement)

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Relative Jump Instructions JR d, Jump relative unconditionally JR Z, d jump relative if Z = 1 JR NZ jump relative if Z = 0 JR C, d jump relative if CY = 1 JR NC, d Jump relative if CY = 0

There are no relative Jump instructions based on Sign and Parity flags

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Instructions related to Index Registers

LD IX, 16-bit load 16-bit data into IX register LD (IX+d), 8-bit load 8-bit into memory location

(IX+d) LD r, (IX + d) copy from memory (IX+d) location

into r LD (IX+d), r copy from r into memory (IX+d) ADD A, (IX+d) add contents of memory (IX+d) into

A SUB (IX+d) subtract contents of memory IX+d from

A

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Instructions related to Index Registers

INC IX Increment 16-bit contents of IX INC (IX+d) Increment contents of

memory IX+d DEC IX decrement 16-bit contents of IX DEC (IX+d) decrement contents of

memory IX + d

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Example

Write instructions to read incoming data from input port INPORT , count the number of readings , and add the readings. When the sum exceeds FF, stop reading the port, store the number of readings added in memory location OUTBUF , and display 01 at the output port OUTLED to indicate the overload?

See page 200 for the answer

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