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PC Assembler

PC Assembler. Ing. E.E. Mak MSc. Cluster1. Introduction Microprocessors Numbers, Binary, Hexadecimal, ASCII Adding and subtracting Instructions and Flags Deeds Z80 simulator. Computer Lay-out. MEM data+instructions. I/O. External. CPU. Model CPU. PC. R1. R2. M A R. A. B. IR.

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PC Assembler

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  1. PC Assembler Ing. E.E. Mak MSc

  2. Cluster1 • Introduction • Microprocessors • Numbers, Binary, Hexadecimal, ASCII • Adding and subtracting • Instructions and Flags • Deeds Z80 simulator

  3. Computer Lay-out MEM data+instructions I/O External CPU

  4. Model CPU PC R1 R2 M A R A B IR ALU M D R DECODER SR C ICU TIMER CLOCK

  5. Main registers. Alternative registers. Accumulator Registers Interupt register Alternative Registers Memory Refresh Adress Registers Z80 Processor Register Layout I A’ A F F’ R W Z W’ Z’ B C B’ C’ D E D’ E’ Flags 8 bit H L H’ L’ S Sign Z Zero I X - - H Half-Carry I Y - - S P P/V Parity/overfl. P C N Negate C Carry

  6. Negative Numbers Using the 8-th bit as a SIGN bit 53 = 0 0 1 1 0 1 0 1 -53 = 1 0 1 1 0 1 0 1 Inverting the bits 53 = 0 0 1 1 0 1 0 1 -53 = 1 1 0 0 1 0 1 0

  7. Two’s Complement 13 0 0 0 0 1 1 0 1 inv 1 1 1 1 0 0 1 0 1 +1 Two’s Complement 1 1 1 1 0 0 1 0

  8. Packed Decimals binary 0 0 1 1 0 1 0 1 53 = Binary packed decimal 0 0 1 1 0 1 0 1 5 35 = 3

  9. Addition 1 0 1 0 0 0 0 1 0 1 0 0 0 1 0 1 + 1 1 1 0 0 1 1 0

  10. Subtraction 1 1 1 0 0 1 1 0 0 1 0 0 0 1 0 1 - 1 0 1 0 0 0 0 1

  11. Flags • Carry • Overflow • Zero • Negative • .. • … • ...

  12. Generic Instructions • Input/output data • Load a value(register) into a register • Arithmetic • jumping / subroutine • control • Bitwise operators : Boolean, Register shifts • interrupt handling • stacking

  13. Example programs LD A,86d ADD A,57d LD A,86d ADC A,57d

  14. Example programs2 Adding 57 to HL: LD A,L ADD A,57d LD L,A LD A,H ADC A,0 LD H,A

  15. Assignments 1. Write a program to store 100 into DE and 385 into BC ADD thereafter DE and BC into HL 2. Investigate substraction using negative numbers for all number-configurations demonstrated in previous sheets 3. Investigate how to multiply using binary numbers 4. Investigate using shift operators could facilitate the multiplication process. 5. What are floating point decimals , how are they implemented?

  16. links • Simple reference list Z80 opcodes: • http://www.ticalc.org/pub/text/z80/z80.txt • Lots of information about the Z80 • http://www.z80.info/ • full reference list op-codes Z80: • http://www.ticalc.org/pub/text/z80/z80_reference.txt • Crash-course Z80 assembly-programming • http://www.ticalc.org/pub/text/z80/z80asmg.zip

  17. Binary Packed 0E 0 0 0 0 1 1 1 0 1A 0 0 0 1 1 0 1 0 + 28 0 0 1 0 1 0 0 0 The use of half bytes let us express two adjacent hexadecimal numbers. As a consequence, we may use this two-digit hexadecimal byte presentation to perform calculations as well, whereas the carry-mechanism while adding work accordingly In hexadecimal coding, each digit of one halfbyte represents a hexadecimal number

  18. Binary Packed Decimal 07 0 0 0 0 0 1 1 1 17 0 0 0 1 0 1 1 1 + 24 0 0 1 0 0 1 0 0 The use of half bytes for numbers 0..9 only, forces while adding special corrections to facilitate adding of these decimal numbers. (What would the result have been without this corrections?) Could you develop an algorithm to make this corrections?

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