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Questions tagged [z80]

For questions regarding the Zilog Z80 microprocessor

7
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2answers
301 views

How costly is it to put things on the stack with the Z80?

Programming languages like C, where any function has the potential to be called recursively, are effectively designed on the assumption that it's okay for all local variables to go on the stack. On ...
13
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2answers
3k views

Why was the 6809 so expensive?

The 6809 was released in 1978, but looking at the usual source for price quotes for old computer components, Byte magazine, I cannot find any quotes for 1979. December 1980 lists it at $38, compared ...
3
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1answer
185 views

Can anyone help provide more information regarding an operating system called I/OS by Infosoft in the early 1980's?

The title pretty much says it all. I'm looking for information about an operating system called I/OS by a company called Infosoft in the early 1980's. I think it might have been a CP/M variant and ...
25
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10answers
7k views

Did anyone ever use the extra set of registers on the Z80?

The Z80 has the surprising feature of a second set of registers. I suppose these were intended to be used for rapid task switching or interrupt handling, though I think if I were programming a Z80 ...
3
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3answers
488 views

Z80 16-bit I/O port addresses

The Z80 indirect I/O instructions are a little quirky: the instructions with the standard mnemonic in r, (c) (where r is a stand-in for any of the normal registers) actually puts the register pair bc ...
7
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3answers
353 views

Role of the Z80 co-processor in GBA games

The Nintendo Game Boy Advance had a Z80-like processor which was typically used for backwards compatibility with GB and GBC games. According to its Wikipedia page, an uncited comment claims that the ...
5
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4answers
226 views

What stops an IO device from driving the databus longer than the CPU expects?

For example, consider the case of handling an INT interrupt signal in the Z80. When the CPU makes the IORQ signal active, it expects the requesting IO device to place a vector onto on the databus. And ...
6
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2answers
395 views

Hardware multipliers on classic CPUs

Can anyone offer some back-of-envelope sort of estimates of what sort of gate count was needed to add a multiplier to 8-bit CPUs? I ask because I find it a bit odd that the 6809 had one, but none of ...
5
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6answers
366 views

What Video Chips/Video generation techniques are usable for the Z80?

I'm building a Z80 home computer and I need color graphics for it similar to other home computers such as the C64. I thought that, like Motorola or MOS, Zilog would have a peripheral chip dedicated ...
2
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3answers
304 views

TI-86 sound capabilities

Is TI-86 calculator capable of producing sounds? In what ways the sound is produced (like timers, beeper bits or alike) if yes? If no, are there any mods that add this capability?
2
votes
3answers
606 views

How can a Z80/8080/6502 use VGA?

I've come across a couple of projects that manage to get VGA working with the Z80 and similar CPUs: Veronica (6502 CPU, VGA signal generation by AVR) ZC160 (Z80 CPU, VGA signal generation by GAL) c-...
0
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1answer
412 views

Why did TI-8x calculator series use the Z80 processor?

Many early Texas Instruments calculators used a Z80 processor. The Z80 is notoriously limited when it comes to mathematical calculators. For example, while it can do addition, multiplication must be ...
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4answers
3k views

Why is the Z80's supply pin in the middle of the data pins?

I recently came across this question, Why are IC pinouts often so illogical?, which asks: Another example - the Z80's data bus: I mean, that one just makes no sense to me whatsoever. Not ...
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3answers
2k views

What are the registers W and Z inside a Z80?

Looking at the Z80's architecture diagram, there is the obvious register file in pink near the middle of the diagram. But four of those registers are not usable by programmers. Those are W, W', Z and ...
26
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4answers
8k views

How did 8 bit processors perform 16 bit arithmetic?

How did 8 bit processors such as the Z80 and 8080 perform 16 bit arithmetic? They have an 8 bit data bus, so how does the ALU perform 16 bit arithmetic on the register pairs? Z80 architecture diagram ...
22
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4answers
2k views

Why does the Z80 include the RLD and RRD instructions?

The Z80 has an instruction RLD, which apparently treats the lower 4 bits in the accumulator and the full 8 bits in (HL) as a twelve bit integer which it then rotates left by 4 bits. The carry flag ...
5
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3answers
404 views

Which Z80 opcodes can I use without a stack?

Quick question, as the title implies. I'm in the process of writing an 'OS' for my DIY Z80 computer and one of the things I need to do to help debug any issues during the boot process is send a ...
8
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2answers
2k views

Did Microsoft BASIC ever use Z80 only instructions?

Did Microsoft BASIC (or any of the OEM versions) ever use Z80 only instructions? For the purposes of this question I'm ignoring the equivalent of BIOS I/O layers which OEMs would have provided.
8
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1answer
393 views

Is S-100 alive?

1) Is S-100 still supported or available for serious home brew? Does anyone still actively sell new boards, cases, designing, support, etc? If not, then about what year did S-100 development stop? 2) ...
15
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1answer
379 views

Zilog's relationship with Mostek

The Wikipedia page on Mostek, one of the original fabricators of Z80 chips, includes the following claim: When Vin Prothro, President, and L. J. Sevin, Chairman of the Board, discovered that ...
55
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8answers
13k views

Why do C to Z80 compilers produce poor code?

When reading some other questions about compiling C for the Z80, How much benefit should be expected on a more advanced compiler for z80/r800 based computers? Native C compiler for Sinclair ZX ...
4
votes
1answer
235 views

Can't get the AY-3-8913 sound chip to work with my z80 (added schematic)

I'm trying to get the ay-3-8913 sound chip to work with my z80 but so far I haven't gotten any sound output yet. I know the chip, my amp circuit and the clock circuit work because it works when I ...
6
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1answer
501 views

Z80 ctc gold ICs speed

Does anyone have any information on what is the maximum speed for the gold ceramic z80 CTC?
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3answers
2k views

Why do only the low 7-bits of the R register increment?

On the Z80 the R register is 8 bits wide, as evidenced by LD A,R and LD R,A And every M1 cycle, R increments by 1. But the uppermost bit does not participate in this increment. R will not go from 0x7F ...
8
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2answers
356 views

ZX BASIC REM statement overhead

Since my other question has been answered and has given me a way to do high-precision timing, I've been experimenting with it a bit. The first thing I did was write a simple benchmark using the FRAMES ...
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4answers
1k views

Uptime in ZX BASIC

How can I obtain the uptime of a Sinclair ZX Spectrum machine (ZX48, ZX128, or Pentagon clone) via their BASIC interpreter? Specifically, the same value used by RANDOMIZE 0 to seed its PRNG. I would ...
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4answers
488 views

What are some example uses of the Z80's BUSRQ/AK pins?

What are some examples of devices that would use the Z80's bus request input? From the technical manual re. BUSRQ: Input, active low. The bus request signal is used to request the CPU address bus, ...
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3answers
1k views

Z80 x 6502 raw performance

A lot have been said in the internet about the 6502 at 1MHz being roughly equivalent in performance to the Z80 at 4 MHz. Is said that the Z80 have a typical 4 clock ticks per instruction while the ...
4
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4answers
449 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 ...
6
votes
1answer
268 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 ...
8
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3answers
1k 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 ...
29
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4answers
5k 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 ...
5
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1answer
595 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 ...
4
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1answer
353 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 ...
16
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4answers
3k 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 ...
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3answers
569 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: ...
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7answers
5k views

Fastest CP/M Z80-based computer ever built?

What was the fastest CP/M computer 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 ...
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4answers
3k 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 ...
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5answers
1k 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 ...
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3answers
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 ...
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4answers
3k 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 ...
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2answers
1k 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 ...
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9answers
2k 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?
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5answers
2k 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 ...
22
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1answer
2k 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 ...
16
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3answers
1k 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'...
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6answers
729 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 ...
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2answers
454 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 ...
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2answers
466 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 ...
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3answers
1k 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?