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

MEMdata+instructions

CPU

I/O External

Model CPU

PC R2R1

IR

M

A

RM

D

R

ALU

A B

SR DECODER

ICU TIMER

C

CLOCK

Z80 Processor Register Layout

Main registers. Alternative registers.

S

Z

-

H

-

P/V

N

C

Sign

Zero

-

Half-Carry

-

Parity/overfl.

Negate

Carry

Flags 8 bit

Adress Registers

Accumulator Registers

Interupt

register

Memory

Refresh

Alternative Registers

W’B’

H’D’

Z’C’

L’E’

WB

HD

A F’FA’

ZC

LE

I

R

I XI Y

S PP C

Negative Numbers

0 1 11 0 1 0053 =

1 1 11 0 1 00-53 =

Using the 8-th bit as a SIGN bit

0 1 11 0 1 0053 =

1 0 00 1 0 11-53 =

Inverting the bits

Two’s Complement

0 0 10 1 1 00

1 1 01 0 0 11

13

1

1 1 01 0 0 11

inv

+1

Two’s Complement

Packed Decimals

0 1 11 0 1 00

3 535 =

0 1 11 0 1 0053 = binary

Binary packed decimal

Addition

1 1 10 0 0 00

0 0 10 0 1 01

1 1 00 0 1 11

+

Subtraction

1 1 10 0 0 00

0 0 10 0 1 01

1 1 00 0 1 11

-

Flags

• Carry

• Overflow

• Zero

• Negative

• ..

• …

• ...

Generic Instructions

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

Example programs

LD A,86d

ADD A,57d

LD A,86d

ADC A,57d

Example programs2

Adding 57 to HL:

LD A,LADD A,57dLD L,ALD A,HADC A,0LD H,A

Assignments1. 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 forall number-configurations demonstrated in previoussheets

3. Investigate how to multiply using binary numbers

4. Investigate using shift operators could facilitatethe multiplication process.

5. What are floating point decimals , how are they implemented?

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

Binary Packed

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

0E

0 1 00 1 0 00

0 0 01 1 0 10

0 0 00 1 1 10

+1A

28

In hexadecimal coding, each digit of one halfbyte represents a hexadecimal number

Binary Packed Decimal

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?)

07

0 1 00 0 1 00

0 0 11 0 1 10

0 0 10 0 1 10

+17

24

Could you develop an algorithm to make this corrections?