Another Home-Brew - Z180

General "chat", not necessarily MTX related
Bill B
Posts: 259
Joined: 26 Jan 2014 16:31

Re: Another Home-Brew - Z180

Post by Bill B »

Martin A wrote: 19 Jun 2020 22:09 Sheesh that's a lot of work to get the CPLS programmed!
Since the whole project is just a pass-time anyway, what does it matter :roll:

Besides, I learn stuff along the way.

I once discovered a "T" rating for projects:

T0: A project that you can complete with existing tools.
T1: A project where you first have to make the necessary tools.
T2: A project where it is necessary to make the tools needed to make the tools required for the project.
Tn: A project where it is necessary (to make the tools needed)*(n-1) to make the tools required for the project.

I have been unable to re-discover the reference for this.
Martin A
Posts: 464
Joined: 09 Nov 2013 21:03

Re: Another Home-Brew - Z180

Post by Martin A »

Bill B wrote: 20 Jun 2020 11:21
Martin A wrote: 19 Jun 2020 22:09 Sheesh that's a lot of work to get the CPLS programmed!
Since the whole project is just a pass-time anyway, what does it matter :roll:

Besides, I learn stuff along the way.
And the learning is the important thing really.
Bill B
Posts: 259
Joined: 26 Jan 2014 16:31

Re: Another Home-Brew - Z180

Post by Bill B »

It lives :)
20200625_142727.jpg
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20200625_142759.jpg
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Some very minimal firmware (source attached):
  • Configures one of the serial ports for input and output
  • Performs some basic memory tests
  • Echoes text typed in
  • Uploads and executes hex files
This last feature will allow me to do further software development and testing without having to repeatedly swap the ROM chip in and out. If I have got the design right, I should even be able to upload programs which re-flash the ROM in-situ.

A couple of hiccups:
  • I should have included a capacitor on the reset line. It is necessary to hit the reset button after powering up to get any reponse. Easy enough, but messy, to solder a capacitor underneath the board. Not so easy, but probably possible, to put one in on the top surface.
  • The processor is currently running at only 4MHz. The small green board in the corner is a home-made oscillator module. When I first started this project, my Z80 databook indicated that I needed an oscillator at twice the CPU frequency. I did not realise that more recent Z180s had clock doubling capabilities. I therefore purchased a couple of 40MHz oscillator modules. I am not sure whether these are proving unreliable, or just that my old test equipment cannot cope with frequencies that high. I need to purchase some new oscillator modules.
Attachments
Z180_EC_Firmware_v1.zip
(4.34 KiB) Downloaded 70 times
Martin A
Posts: 464
Joined: 09 Nov 2013 21:03

Re: Another Home-Brew - Z180

Post by Martin A »

It's a great feeling when that happens. Well Done :D

I've checked the Z180 board I did for the MTX plus, that's got a 12mhz clock on it so I suspect I ran that clock doulbed. It's a long time since I played with it, though I do remember trying all sorts of clocks, I think it was more stable at 12 doubled than it was at 25 without the clock doubler (there are no 24 mhz clocks in the box).

Interestigly it's got a stock 10mhz CTC on it which would have been out of spec at 12, let alone 24. That may well be the reason fot the upper limit of the board being in the 24-25 range.

Hopfully when you get sone clocks, you'll be able to surpass the 20mhz rating of the CPU itself.
Bill B
Posts: 259
Joined: 26 Jan 2014 16:31

Re: Another Home-Brew - Z180

Post by Bill B »

The Z180 I am using is rated at 33MHz. I will probably get 10MHz and 16MHz oscillator modules.
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