SamusDrake
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A Pi using an external Zilog Z80 chip

Mon Jun 05, 2017 9:52 pm

Hello all. Just popping in for a bit of guidence...

After 17 years of programming, I'm finally making an effort to learn Assembly in order to strengthen my C skills - and for other things. I have a strong interest in much older chips such as the Motorola 68000 and the Zilog Z80. My skill with electronics is practically non-existant.

I've noticed on the Farnell/Element 14 site, much to my surprise, that these old chips are still on the market. So I'm wondering if this would be a sensible first project; Using the GPIO pins on the Raspberry Pi to connect to a Z80 chip so that I could have the pi send the Z80 instructions, have it process them and return data to the Pi. I assume such as set up would save having to build a computer from scratch?

Another question is what other components would I need other than just a Pi and Z80 chip?

Cheers.

Heater
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Re: A Pi using an external Zilog Z80 chip

Tue Jun 06, 2017 12:27 am

I can't help thinking that you would have a much nicer time of it by getting hold of an actual Z80 board.
For example the RC2014 Mini - Single Board Z80 Computer Kit:
https://www.tindie.com/products/Semacht ... puter-kit/

I saw that board at the Bay Area Maker Faire and had a long chat to it's creator. It's a very nice looking board.

klricks
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Re: A Pi using an external Zilog Z80 chip

Tue Jun 06, 2017 4:44 am

SamusDrake wrote:... Another question is what other components would I need other than just a Pi and Z80 chip?....
You would need just about everything listed in the kit that Heater posted above.
Note the site mentions using a RPi Zero to get HDMI and USB.
Any interface to/from the RPi would need have level translate circuits. 3V3 to 5V
You could easily communicate from RPI to Z80 over serial 3 wires. (via UART on the Z80 board)
IMO it would be possible but not feasible to attempt to interface the RPi to D0-D7 and A0-A15 etc.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

SamusDrake
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Re: A Pi using an external Zilog Z80 chip

Tue Jun 06, 2017 6:43 am

Well, I'd have to learn how to solder, but I really like that kit! And if I only need a Pi Zero for output and keyboard input, its right up my street.

Thank you very much for the assist!

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TonyD
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Re: A Pi using an external Zilog Z80 chip

Tue Jun 06, 2017 12:04 pm

Heater wrote:I can't help thinking that you would have a much nicer time of it by getting hold of an actual Z80 board.
For example the RC2014 Mini - Single Board Z80 Computer Kit:
https://www.tindie.com/products/Semacht ... puter-kit/

I saw that board at the Bay Area Maker Faire and had a long chat to it's creator. It's a very nice looking board.
I agree with Heater's comments about using something like the RC2014 Z80 kit.

The RC2014 guy was at Maker Faire UK back in April and was a nice guy to talk to.

If you want something more Pi shaped check out Z-Berry:

https://sites.google.com/site/zberrysbc/

A Z80 Single Board Computer using a PCB footprint very similar to the Pi
Tony

Martin Frezman
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Re: A Pi using an external Zilog Z80 chip

Tue Jun 06, 2017 12:08 pm

It'd be super-keeno if someone would go ahead and build an actual, usable computer using the RC2014 and a Pi-Zero and report back here exactly what he did and how, so that the rest of us could do likewise.

The website (which I've read) implies that it can be done, but is, of course, short on actual details.
If this post appears in the wrong forums category, my apologies.

SamusDrake
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Re: A Pi using an external Zilog Z80 chip

Thu Jun 08, 2017 10:44 pm

Theres certainly more options than I expected for Z80 home projects.
I've been weighing up the ZX Spectrum Next as well, as I started computing as a child back in the early 1980s with the 48K+, but I have a feeling thats going to be expensive...

I do have one last question, to save opening another thread. I'm confused as to the audio hardware of the Raspberry Pi itself - does it have a dedicated sound chip, like say the C64 had the SID, or does the PI generate sound in software only?

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rpdom
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Re: A Pi using an external Zilog Z80 chip

Fri Jun 09, 2017 5:15 am

SamusDrake wrote: I'm confused as to the audio hardware of the Raspberry Pi itself - does it have a dedicated sound chip, like say the C64 had the SID, or does the PI generate sound in software only?
The HDMI audio is pure hardware in the Broadcom chip. The A/V audio output uses the hardware PWM channels but I believe that is at least partly driven by software.

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PeterO
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Re: A Pi using an external Zilog Z80 chip

Fri Jun 09, 2017 7:39 am

That looks fun :-)

The last Z80 system I built consisted of just a Z80 and 128K of RAM and a PIC.

The PIC had a serial interface back to a PC and could also act as a Z80 bus master using BUSREQ/BUSACK. The PIC downloaded the bootstrap code into the Z80 and started it running. The Z80 could signal the PIC when it needed a peripheral action by writing a command block into RAM and then writing to the PIC's parallel port. The PIC then read the command block from RAM, passed a command up the serial i/p to the PC, and wrote results back into the RAM and set the "done" flag in the command block.

I had sources for a Z80 CP/M BIOS, and some 8" floppy image files with CP/M 2.2 in them which I was able to boot :-)

PeterO
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"The primary requirement (as we've always seen in your examples) is that the code is readable. " Dougie Lawson

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PeterO
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Re: A Pi using an external Zilog Z80 chip

Fri Jun 09, 2017 7:42 am

Martin Frezman wrote:The website (which I've read) implies that it can be done, but is, of course, short on actual details.
All the details are there, of course you just haven't found them !

PeterO
Discoverer of the PI2 XENON DEATH FLASH!
Interests: C,Python,PIC,Electronics,Ham Radio (G0DZB),1960s British Computers.
"The primary requirement (as we've always seen in your examples) is that the code is readable. " Dougie Lawson

SamusDrake
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Re: A Pi using an external Zilog Z80 chip

Sat Jun 10, 2017 10:38 pm

Thanks to all who have replied.

Cheers!

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scruss
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Re: A Pi using an external Zilog Z80 chip

Sun Jun 11, 2017 3:34 am

If you didn't want to immediately get into the hardware, you can run simh on your Raspberry Pi. It includes a very capable Z80 emulator.

There are other homebrew machines out there besides the RC2014. I have the very easy to build Zeta SBC V2, and there's also the very tiny Z80 Membership Card.
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