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Old 10th Nov 2021, 2:38 pm   #1
Phil__G
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Default Grant Searle's retro "Simple Z80" 32k enhancement

For anyone who's built the 'BASIC-only' Grant Searle 32k Simple Z80, I've done a new rom image that integrates a small 'period-appropriate' machine code monitor.
The file and a brief document can be found on http://philg.uk in the Retro section. Here's a slightly out-of-date video, its since been tidied up a bit:

https://youtu.be/mvZ_L-rdgBQ

Cheers
Phil
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Old 16th Nov 2021, 10:08 pm   #2
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Default Re: Grant Searle's retro "Simple Z80" 32k enhancement

I did manage to get mine working fine and it is a great addition - well worth adding to these machines. Thanks Phil.
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Old 17th Nov 2021, 7:51 pm   #3
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Default Re: Grant Searle's retro "Simple Z80" 32k enhancement

Quote:
Originally Posted by Timbucus View Post
...it is a great addition - well worth adding to these machines
Thanks very much Tim

Today I did a rom image with these enhancements for the 56k version of the board - its untested as me, Tim & Jeff all use the 32k version but I'm sure it will be ok as the difference is only a couple of addresses. Its on the Retro page of philg.uk
I'd be interested to hear if anyone does give it a try
Cheers
Phil
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Old 15th Dec 2021, 8:52 pm   #4
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Default Re: Grant Searle's retro "Simple Z80" 32k enhancement

I finally got around to building a 56k version of the Grant Searle Simple Z80 just to try my revised ROM as I'd posted it without testing it on the 56k version. It works great - but I do miss the NVRAM I have on the 32k ones... I'll see if I can afford a 128k x 8 NVRAM
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Old 24th Dec 2021, 2:09 am   #5
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Default Re: Grant Searle's retro "Simple Z80" 32k enhancement

Well, I pushed the boat out and bought a DS1245Y 128k x 8 NVRAM from RS, it works great and gives me two separate, manually-switched 56k non-volatile RAM pages, one to play with BASIC and M/C, and one page dedicated to Star Trek !!! Conversion details are documented on http://philg.uk in the 'Retro' area - theres a small mod as the DS1245Y has no 'true' chip-select. Thinking I might try four 32k pages, could be more useful... on these small systems with no storage, NVRAM is really convenient
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Old 24th Dec 2021, 11:22 am   #6
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Default Re: Grant Searle's retro "Simple Z80" 32k enhancement

Pushing forward the frontier - warping Star Trek into a different dimension - well done Phil.
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Old 28th Dec 2021, 8:25 pm   #7
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Default Re: Grant Searle's retro "Simple Z80" 32k enhancement

Prices are sky-high at the moment and my initial reaction was that £35 seemed an expensive nicety - but this is 128k x8, non volatile...
my Nascom-1 32k RAM-A memory board plus the essential bufferboard was over £200 in 1979 and was nowhere near as reliable as this!
I think £35 is a bargain in comparison!
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Old 7th Jan 2022, 1:20 pm   #8
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Default Re: Grant Searle's retro "Simple Z80" 32k enhancement

That's very interesting Phil. It's making me want to start building! I was familiar with Grants pages but I've got so many things on the go ...

John
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Old 7th Jan 2022, 3:41 pm   #9
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Default Re: Grant Searle's retro "Simple Z80" 32k enhancement

PM your postal address John and I'll send you a PCB, FOC.
Let me know if you have a 7.3728 crystal and the 22pfs.
Its a 10 minute build, and works great, a nice little system!
I found a cheap but very neat case on RS, see pics
https://uk.rs-online.com/web/p/gener...osures/2006674
Internally just a few mm larger than the board, fits perfectly.
Cheers
Phil
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Old 7th Jan 2022, 10:05 pm   #10
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Default Re: Grant Searle's retro "Simple Z80" 32k enhancement

Thank you very much Phil. PM sent.
My efforts at building Z80 machines started and finished here:

https://www.vintage-radio.net/forum/...32#post1283032

I don't have the crystal but happy to go and buy one and the 22pFs.

John
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Old 13th Jan 2022, 1:17 pm   #11
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Default Re: Grant Searle's retro "Simple Z80" 32k enhancement

Well, thank you very much for the PCB and crystal etc Phil. Very much appreciated. I have often thought about building Grants Z80 retro computer and you've given me the push I needed.

Some worthwhile enhancements there. The DS1233 for power up reset and debouncing the reset switch is a very good idea and something I've used before.

I'm collecting together the bits I haven't got at the moment so when it's running, I'll let you know.

Thanks again.

John
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Old 15th Jan 2022, 9:18 am   #12
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Default Re: Grant Searle's retro "Simple Z80" 32k enhancement

I've been looking in detail at Grants Z80 SBC. I see that he uses a 7.3728MHz crystal so that the baud rate timing is correct for the UART, an MC6850. He uses a 4MHz Z80 and overclocks it and says that while he hasn't found a 4MHz one that didn't work he recommends a 6 or 8MHz part.

He also recommends an MC68B50 which is faster than the MC6850 or the MC68A50. The MC68B50 is very expensive! I have a MC6850 and if I use that, I'll be overclocking it!

So what do I do, use a 3.6864MHz crystal and bring the baud rate down to 57600 baud or try and overclock the 6850.

What I didn't really want to do is solder in the 7.3278MHz crystal and then find I have to remove it and use a 3.6864MHz one.

Something to think about!
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Old 15th Jan 2022, 10:39 am   #13
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Default Re: Grant Searle's retro "Simple Z80" 32k enhancement

I used a 6850P Motorola part and it works fine with the 7.3 crystal... YMMV
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Old 15th Jan 2022, 10:42 am   #14
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Default Re: Grant Searle's retro "Simple Z80" 32k enhancement

Hi John, the 6850 should be fine, Z80 I/O timing includes a wait state,
plus the 6850 in its native 68xx environment syncs to the E signal halfway through the cycle so you could say its twice as fast as the spec.

One of my own 4mhz z80s was ok at 7 but I only tested one, I had a few 10mhz parts from RS
Cheers
Phil
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Old 15th Jan 2022, 11:09 am   #15
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Default Re: Grant Searle's retro "Simple Z80" 32k enhancement

Thanks for that Phil and thank you Timbucus. Armed with that information. I'll carry on with the 6850. I've been looking through my Z80 parts and I have a 6MHz one that I didn't know I had so I'll use that.

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Old 17th Jan 2022, 1:20 am   #16
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Default Re: Grant Searle's retro "Simple Z80" 32k enhancement

Hi John, I've assembled four of Jeff Tranter's Z80 PCBs now, two 32k and two 128k. I couldnt remember so I opened them up & checked (they're all cased) and throughout I've used 6850's, ie not 'B' chips. All four have been in use almost continually for several weeks with no problems.
Go for it

Forgot to say earlier, those RS cases are perfect but you need to orient the CH340G pins under the board rather than outward, like the pic on the right:

Cheers
Phil
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Old 17th Jan 2022, 9:05 am   #17
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Default Re: Grant Searle's retro "Simple Z80" 32k enhancement

Thanks Phil. I'll stop worrying about it now! One thing I didn't have was a 24 pin socket but that should arrive today or tomorrow.

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Old 22nd Jan 2022, 9:14 am   #18
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Default Re: Grant Searle's retro "Simple Z80" 32k enhancement

Finally got it working! Thanks again Phil_G. If you hadn't sent me the PCB I don't know if I'd ever have got round to it even though I'd had my eye on Grant Searles pages.

You'll see in the pictures I did use the 1MHz 6850 and a 6MHz Z80.

John
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Old 22nd Jan 2022, 1:20 pm   #19
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Default Re: Grant Searle's retro "Simple Z80" 32k enhancement

Lovely seeing that 1978 prompt!
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Old 23rd Jan 2022, 1:34 am   #20
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Default Re: Grant Searle's retro "Simple Z80" 32k enhancement

Absolutely Tim, I love it, its so Nascommy, even the Teraterm font is right

Thanks for posting that John, great to see another board put to use.
On all the CH340G USB/serial adapters I have, RTS doesnt appear to work so in Teraterm I have to add a delay after every line, 200-300ms works ok even for long programs like Star Trek. One day I'll investigate why properly but you know how it is. Yours might handshake ok, it could be just my adapters I dont know

Cheers
Phil
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