The KC-85 and the U880The KC-85 and the U880

Team members:

Nadine Spörl

Angela Roggan

Martin Burkard

Alexander Becker

Kompakt Computersystem KC 85 series1984-1990 in the GDR

KC 85/1(Z9001)

• Keyboard computer

• Basic

Module

Interpreter

KC 85/2(HC 900)

• Can use different OS

KC 85/3

• BASIC as programming language in ROM

KC 85/4

• 1 basic device

• Improvement

Graphic

Sound

• Can be extended

• 2 module slots

• Separate keyboard

Upgrade the system• plug in modules

• further interfacesParallel ports

Serial ports

RAM

ROM

Operating System

• CAOS (Cassette Aided Operating System)

Loading/storing data via tape recorder interface

• Add-on devices

Bus driver: extends the number of module slots by 4

Floppy disc expansion: a second U880 systemaccess to up to 4 floppy disc drives

IDE interface

• 8-bit (16-bit) load instruction

• Stack instruction

• Exchange instruction

• Block look-up and transfer instruction

• 8-bit (16-bit) arithmetic instruction

• Branch and subroutine instruction

• Rotation and shift instruction

Instruction set

Registers

Name B,C,D,E,H,L,W,Z

P (or F)

R

I

IX,IY

PC

SP

Type

general purpose registers

Processor Status register

Memory Refresh register

Interrupt Page address

registerindex registers

Program Counter register

Stack Pointer register

Size 8-bit

8-bit

8-bit

8-bit

16-bit

16-bit

16-bit

The internal organization of the U880

Flags

Abbreviation

N

V

1

B

D

I

Z

C

TypeNegative flag

Parity/Overflow flag

UNUSED flag

Break flag

Decimal Node flag

Interrupt Disable flag

Zero flag

Carry flag

Locationbit 7

bit 6

bit 5

bit 4

bit 3

bit 2

bit 1

bit 0

Interrupts

• IRQ (maskable hardware

interrupts)

• NMI (non-maskable hardware

interrupt)

• BRK (software interrupt)

Addressing Modes

• nine different addressing modes– Immediate addressing (8-bit)– Immediate extending addressing (16-bit)– Relative addressing (8-bit)– Extended addressing (16-bit)– Indexed addressing (16-bit + 8-bit)– Register addressing (8-bit)– Register indirect addressing (16-bit)– Bit addressing– Modified page 0 addressing

Addressing Modes

• Immediate addressing (8-bit)

1. The Instruction Register is loaded with the opcode2. The KC85 is incremented3. The data byte, which is pointed at, is read into the U880 CPU4. The instruction is executed5. The result is stored in the accumulator6. The KC85 is incremented and the next instruction is loaded

Addressing Modes

• Immediate extending addressing

– used to load 16-bit registers– instructions therefore have two data bytes– most-significant data bit is read first– stored in the most significant bit of the target

register– KC85 is incremented and these steps are repeated

with the least-significant bit

Addressing Modes

• nine different addressing modes– Immediate addressing (8-bit)– Immediate extending addressing (16-bit)– Relative addressing (8-bit)– Extended addressing (16-bit)– Indexed addressing (16-bit + 8-bit)– Register addressing (8-bit)– Register indirect addressing (16-bit)– Bit addressing– Modified page 0 addressing

Perspective/Role on the Market

Characteristics of the U880/Z80:

• a mid-seventies chip

• only eight bit

• very slow for today's standards

Perspective/Role on the Market

Attractiveness:

• very cheap

• easy to handle for programmers and hardware designers

• 8bit exactly match the bus width of the vast majority of

memories and peripherals on the market

• the chips architecture allows easy integration with on chip peripherals• Tools are widely spread