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Microprocessor

Microprocessor. Dr. Rabie A. Ramadan Al-Azhar University Lecture 8. Z80 Assembly Programming. Arithmetic Operations. Addition and Subtraction Increment/Decrement 1’s and 2’s Complement. Addition and Subtraction. Performed in relation to the contents of the operands .

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Microprocessor

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  1. Microprocessor Dr. Rabie A. Ramadan Al-Azhar University Lecture 8

  2. Z80 Assembly Programming

  3. Arithmetic Operations • Addition and Subtraction • Increment/Decrement • 1’s and 2’s Complement

  4. 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)

  5. 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

  6. 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

  7. 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)

  8. Branch Operations • Jump instructions • Call and return instructions • Restart instructions

  9. 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

  10. 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

  11. 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)

  12. 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)

  13. 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)

  14. 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

  15. 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

  16. 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

  17. 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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