Transcript Lecture 8 - Rabie A. Ramadan

Microprocessor
Dr. Rabie A. Ramadan
Al-Azhar University
Lecture 8
Z80 Assembly Programming
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Arithmetic Operations
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Addition and Subtraction
Increment/Decrement
1’s and 2’s Complement
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Addition and Subtraction
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Performed in relation to the contents of the operands .
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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.
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ADD A, 8-bit  Add 8-bit data directly to the accumulator
(2 bytes).
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ADD A, (HL)  Add memory contents to the accumulator
(1 byte)
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Addition and Subtraction
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SUB r  subtracts the contents of register r
from the accumulator.
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SUB 8-bit  subtract 8-bit from the
accumulator
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SUB (HL)  subtract memory contents from
the accumulator
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Increment/Decrement
Instructions
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INC/DEC r  increment/ Decrement the contents of
register r.
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INC/DEC (HL)  Increment/decrement the contents of
memory
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INC/DEC rp  Increment/ decrement register pair (HL,
DE, BC, SP)
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One byte each
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1’s and 2’s Complement
Instructions
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Performs the complement on the accumulator
contents .
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CPL  1’s complement or inverts the contents of the
accumulator (1 byte)
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NEG  2’s complement. Subtracts the accumulator
from 00 (2 bytes)
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Branch Operations
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Jump instructions
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Call and return instructions
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Restart instructions
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Jump Instructions
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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
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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
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JP C, 16-bit  Jump on carry to 16-bit address (CY=1)
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JP NC, 16-bit  Jump on no carry to 16-bit address
(CY=0)
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JP Z, 16-bit  Jump on zero to 16-bit address (z = 1)
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Absolute Jump
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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
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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
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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
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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
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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
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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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