Questions tagged [z80]

The Zilog Z80 microprocessor. Prefer [game-boy] instead for questions about the Game Boy CPU nicknamed the ‘GBZ80’.

Filter by
Sorted by
Tagged with
38 votes
7 answers
24k views

Comparing raw performance of the Z80 and the 6502

A lot has been said on the internet about the 6502, at 1MHz, being roughly equivalent in performance to the Z80, at 4 MHz. It is said the Z80 has a typical 4 clock ticks per instruction, while the ...
Biff Iam's user avatar
  • 2,159
6 votes
4 answers
2k views

When did the Z80 compatibles reach very high clock speed?

In the early eighties, the Z80B and Z80H at 6 and 8 MHz respectively, were released. In 1985, the Hitachi HD64180 reached 10 MHz (with some enhancements such that it seems to be reckoned the ...
rwallace's user avatar
  • 58.4k
8 votes
1 answer
840 views

Breakeven number of bytes for programmable DMA

Contemporary with the old 8-bit chips, existed powerful but unsung programmable DMA controllers like the Zilog 8410 and the Intel 8257, that could copy data from one memory location to another, much ...
rwallace's user avatar
  • 58.4k
9 votes
4 answers
4k views

How do Z80 Block Transfer instructions work?

I'm familiar with the Hitachi 6309's block transfer instructions (TFM). It can work as a "poor man's" DMA controller or Blitter, and is one of the things that makes the 6309 the best 8-bitter of all ...
Brian H's user avatar
  • 60.1k
43 votes
7 answers
8k views

Did any computers use the Z80B?

The Z80 was one of the most popular CPUs of the seventies and eighties. In almost all cases that I know of, the version used was the Z80A, rated for 4 MHz, sometimes clocked a little slower in order ...
rwallace's user avatar
  • 58.4k
6 votes
1 answer
2k views

How much faster is the Z80H?

The Z80A, rated for a maximum clock speed of 4 MHz, was a very widely used CPU in the 8-bit era. The Z80H, introduced in 1986, was rated for a maximum clock speed of 8 MHz. This would at first glance ...
rwallace's user avatar
  • 58.4k
6 votes
1 answer
588 views

How does the SAM Coupé refresh its RAM?

The SAM Coupé was a ZX Spectrum compatible computer with a 6MHz Z80, 256K RAM minimum, enhanced graphics and sound and an improved BASIC amongst other features. My question is about its memory. The ...
user3570736's user avatar
  • 1,782
29 votes
4 answers
10k views

What's the difference between "opcode" and "instruction" in this Zilog ad?

In a Zilog ad from 1976 comparing the Z80 and Intel 8080, the following table is presented: What is the difference here between "Instructions" and "OP Codes"? In my experience, the two terms are ...
Psychonaut's user avatar
  • 7,023
11 votes
3 answers
1k views

z80 crashes after executing some instructions

I'm building my own Z80 computer but I'm having a very strange problem. Consider this code: ld a,0xaa out (00),a jp a That works as expected, outputting 0xaa on port 0x00. Now consider this code: ...
C32's user avatar
  • 394
44 votes
10 answers
15k views

Fastest non-emulated CP/M Z80-based computer ever built?

What were the fastest CP/M computers ever built? I'll restrict this to the Z80 variant of CP/M, no CP/M-86, CP/M-68k etc. Z80 compatibles with higher clock frequencies or more instructions/clock or ...
dirkt's user avatar
  • 26.1k
25 votes
4 answers
6k views

Z8410 DMA chip as GPU?

There are basically two ways to design a 2D graphics system: Provide lots of hardware support in the form of tiles, hardware scrolling and sprites, to put together each frame on the fly from a small ...
rwallace's user avatar
  • 58.4k
17 votes
9 answers
4k views

Z80 and video chip contending for random access

Back in the 8-bit days, I used 6502 computers, where the story about memory access was easy to understand. RAM chips of the late seventies and early eighties could do 2 MHz (or a bit more e.g. 2.6 in ...
rwallace's user avatar
  • 58.4k
9 votes
3 answers
1k views

Game cartridges on the S-100 bus?

Many Z80 computers in the seventies and early eighties used the S-100 bus, into which you could plug many kinds of expansion cards. Would it have been possible to plug suitably designed game ...
rwallace's user avatar
  • 58.4k
18 votes
4 answers
6k views

How fast is memcpy on the Z80?

I gather the fastest way to implement memcpy (copy a certain number of bytes from one place in memory to another) on the Z80 is to use an instruction called LDIR. But how fast is the result, when ...
rwallace's user avatar
  • 58.4k
26 votes
2 answers
5k views

How did Z80 multiprocessing work in the Namco Galaga hardware?

Galaga was a popular arcade game developed and released by Namco (Midway in N. America) in 1981. It had amazing, fast, smooth 2D-sprite graphics, and relied on Namco hardware that utilized 3 Z80 CPUs ...
Brian H's user avatar
  • 60.1k
15 votes
11 answers
4k views

Commercially available computer with single-step feature?

Was there ever a commercially available hobbyist/teaching computer with the ability to single-step the processor? Maybe a Z80-based machine?
Kenneth Sizer's user avatar
20 votes
5 answers
4k views

Why does the Z80 have a half-carry bit?

The Z80 apparently had a 4-bit ALU, and computes 8-bit values in two stages. The half-carry bit preserves the carry from bits 3 to 4. Why did the designers of this chip choose to preserve that value ...
Omar and Lorraine's user avatar
33 votes
2 answers
4k views

What is the relative code density of 8-bit microprocessors?

When RAM is at a premium, as it was in the old days, a greater code density of an instruction set can be a substantial advantage. (Click saver: Code density refers loosely to how many microprocessor ...
Leo B.'s user avatar
  • 18.3k
27 votes
5 answers
5k views

DIY Project using 1970s 8-bit CPU, is it possible?

I've recently really wanted to try and design a computer system around a retro 8-bit CPU such as the Zilog Z80 or the Intel 8080, and I would appreciate some sanity checks! I was inspired by Ben Eater'...
Zee2's user avatar
  • 373
25 votes
8 answers
2k views

Separate code and data address spaces on the Z80

Reading through the Z80 datasheet, I noticed something interesting. The Z80 separates its instruction execution into separate phases (which are called "machine cycles" in the official literature, but ...
Jules's user avatar
  • 12.8k
9 votes
2 answers
1k views

ZiLOG Z80 fan-out (CMOS version, Z84C0006PEC)

I am building a z80 based 8 bit computer, and I really don't want to fry my chip. I was looking at this datasheet, but I couldn't find the fan-out specified. There are some electrical characteristics ...
Njubster's user avatar
7 votes
2 answers
843 views

Can I power a z180 with 3.3v [closed]

I'm planning to buy a Z8018006PSC. A z180 CPU (which I found is compatible with the z80 and has some advantages, for instance, able to address up to 1MB of RAM). I'm planning to use it together with ...
h0m3's user avatar
  • 155
20 votes
3 answers
6k views

How much did the 6502 and Z80 cost?

It is said that the 6502 was cheaper than the Z80. As of 1978, what were the actual prices of the two chips, in wholesale quantity?
rwallace's user avatar
  • 58.4k
13 votes
1 answer
936 views

When were the various frequency Z80 CPUs introduced?

The Z80 was introduced, as I understand it, at a clock speed of 2 MHz. Later, Z80-based computers at 3.5 MHz started showing up. In what year did this faster clock speed become available? (In ...
rwallace's user avatar
  • 58.4k
6 votes
1 answer
825 views

pop af and flags

I'm writing a Z80 emulator in Swift for Mac OS and I have got as far as implementing the 16 bit pop instruction. The documentation I have found (i.e. The Z80 CPU User manual UM008011-0816 and also ...
JeremyP's user avatar
  • 11.4k
11 votes
1 answer
894 views

On the Z80, how can we use LD instead of JR?

The Galaksija ROM disassembly has a link to "A tutorial on how to use "ld" instructions instead of "jr" and save a few bytes in the process." My question is how does this work! It can see at l038ch ...
Omar and Lorraine's user avatar
19 votes
2 answers
2k views

First computer emulator in Windows

I released my ZX Spectrum emulation Wspecem, and GPL sources first time publicly in the Internet at large, the 15th May 1996, for Windows 95. I am quite sure it was the first ZX Spectrum emulation ...
Rui F Ribeiro's user avatar
8 votes
1 answer
2k views

z80 CPU User Manual AND P/V Flag

I'm writing an emulator for the z80 CPU using the "z80 CPU User Manual" from zilog.com as reference. When I got into the AND operator I got confused. In the Condition Bits Affected is declared "P/V ...
h0m3's user avatar
  • 155
5 votes
2 answers
965 views

What does the blinking of the cpu address bus actually means?

I'm currently running NOP on a Z80A cpu. All it does it flash some led, I expected it to flash 1 by 1. The led are place from address 16-0
user142208's user avatar
1 vote
1 answer
389 views

How to I give instructions to a Z80 CPU [duplicate]

I found a Z80 CPU lying around my house. I've search all over the Internet but I still don't know how do I input stuff and tell it what to do. Help me please
user93228's user avatar
24 votes
3 answers
8k views

Wiring a Zilog Z80

I've recently got hold of an old Zilog Z80 microprocessor and I know how to clock and test it. I do not however know how to connect RAM, I/O ports, control switches (for programming instructions into ...
DevelopedLogic's user avatar
24 votes
4 answers
5k views

How did the Apple II forward binary instructions to the Z80 software card with CPM?

Microsoft produced the Z80 Softcard for the Apple II enabling it to run CPM and many Z80 binary programs. This seems to be an unthinkable achievement. (For a kid who had an Apple IIe but was only a ...
hawkeye's user avatar
  • 2,565
57 votes
8 answers
10k views

How were Western computer chips reverse-engineered in USSR?

The British ZX Spectrum computer had many clones in the Eastern Bloc. It seems many of them were built using Russian-made chips from the Angstrem factory in Zelenograd in/near Moscow. The Russian ...
Omar and Lorraine's user avatar
29 votes
2 answers
5k views

Why did Sinclair choose the Z80 for its range of home computers?

The Sinclair computers are known for their low cost compared with other computers that were popular in the early 1980s. This is why they had membrane keyboards, or that rubber stuff in the case of the ...
Omar and Lorraine's user avatar
49 votes
2 answers
15k views

How did the Z80 instruction set differ from the 8080?

The Zilog Z80 microprocessor, known for its use in the ZX Spectrum, was designed to be a backwards-compatible extension to the Intel 8080 processor. It introduced several new instructions to the 8080'...
wizzwizz4's user avatar
  • 18.5k
27 votes
4 answers
4k views

Use of undocumented opcodes

I figure this is fitting for Retrocomputing.SE because CPUs like the 6502 and Z80 and the PDP-8, and probably others, have undocumented instructions and will happily execute them, in contrast with ...
Omar and Lorraine's user avatar
35 votes
2 answers
3k views

Can the two CPUs in a Commodore 128 run at the same time?

The Commodore 128 has two CPUs. One is some variant of the 6502, and the other is a Z80. One CPU is there for compatibility with the Commodore 64 and the other is there presumably to give basic ...
Omar and Lorraine's user avatar
11 votes
2 answers
2k views

Faulty M1 line on the Z80A

It is well known that some Z80A processors with non functioning M1 signals were assembled into many ZX Spectrums. As this signal is not used in the main board and not everyone bought interfaces that ...
mcleod_ideafix's user avatar
14 votes
5 answers
7k views

Looking for a Z80 simulator/emulator for Linux

I've seen simulators for the 8085 (i.e., sim8085) but not the Zilog Z80. Is there a similar sort of editor/assembler/compiler/debugger simulator for the Z80?
Frank Pittel's user avatar
24 votes
5 answers
3k views

How much benefit should be expected on a more advanced compiler for z80/r800 based computers?

I am self studying about compilers, and get hands on very good textbooks about the subject. I am thinking in develop a compiler using the almighty llvm infrastructure to cross compile to old computers,...
flavio's user avatar
  • 580

1 2 3
4