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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 26th May 2020, 4:27 pm   #41
mikew8760
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Default Re: Maplin Z80 SBC

Final update(?)
Thanks to all of you who helped me sort out the MICE. It has turned out to be a failed 1489 section that controlled the CTS pin on the 8251. To me an odd arrangement, but then I have little experience of RS232 circuits. The 1489 is driven by a section of the 1488, which is controlled in turn by another section of the 1488.
So, replacing the 1489 cured the fault, so now hopefully back on track to probe more deeply into the Maplin SBC.
Again, many thanks to all.
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Old 26th May 2020, 4:44 pm   #42
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Default Re: Maplin Z80 SBC

Does this same 1489 receiver IC handle the RS232 RX input line as well?

If so you may find that after replacing that IC, the RX input is now able to work directly with the TX output from the USB-serial lead.

I'm wondering if the RX input was half-damaged all along.
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Old 27th May 2020, 1:43 pm   #43
mikew8760
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Default Re: Maplin Z80 SBC

I hadn't thought of that as a possibility, but I'm glad you mention it! Yes, the USB-TTL adapter indeed does now work!! Seems strange that the original line receiver would not accept TTL, but did on +/- 12v. Well done, you should be awarded a Gold Star....
Once again, many thanks for all your inputs.
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Old 22nd Jun 2020, 3:04 pm   #44
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Default Re: Maplin Z80 SBC

Thanks to all those who have been of great help in my getting this old SBC, and the ancient Emulator, to work.
Now I am in need of some further assistance, and again hoping someone can point me in the right direction.
I'm no Jerry Walker, so my next wish is to find a simple, cheap Z80 assembler/cross-assembler so I can create some programs in place of the M12 EPROM code. Preferably, a utility that will run under Windows, XP or Win10, rather than via the PowerShell. I feel there must be something out there, but I haven't found it yet.
Ideally, of course, I'd prefer a GUI IDE with a C compiler, but that's doubtless a bridge too far? I have 'looked' at the Github SDDC, but have to confess that my failing mental capacities are unable to get to grips with it.

Once more, all and any suggesition welcome, except those recommending I get a Spectrum!
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Old 22nd Jun 2020, 4:15 pm   #45
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Default Re: Maplin Z80 SBC

For other systems being discussed here some of us are using 'SB-Assembler 3' which is a free open source cross assembler written in Python by San Bergmans whose hobby electronics website is here:-

https://www.sbprojects.org/

Scroll down the page and you see a link to SB-Assembler and click through on that for more information and a download.

However, that one is probably more command-line than you would like. Others may know of a Windows GUI-based Z80 assembler / IDE?
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Old 22nd Jun 2020, 6:37 pm   #46
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Default Re: Maplin Z80 SBC

For a windows based Z80 assembler this one - ZEUS - looks potentially promising - written by one of the three man team who were 'Design Design' and produced such off beat Spectrum titles as 'Halls Of The Things'.

http://www.desdes.com/products/oldfiles/zeus.htm

There was a native assembler for the Spectrum called ZEUS (which I had) and it may well have been the forerunner of this Windows version, written by the same team. There's also a companion disassembler ('Diana', naturally).
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Old 22nd Jun 2020, 7:47 pm   #47
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Default Re: Maplin Z80 SBC

Yes ZEUS is by Simon and it the descendent. Several of the Next team use it as it has a built in Z80 emulator to allow you to test a lot of code off machine.

I use the Z80ASM from Z88DK which is a C compiler that can target a huge range of 8 bit machines so is great for bigger projects if you are experienced in C. That is very command line and probably not the best choice for the OP
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Old 6th Jul 2020, 10:18 am   #48
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Default Re: Maplin Z80 SBC

Now, here's a funny thing; not directly related to the Maplin SBC, but might be of interest to others.
I have a Minipro TL866 programmer which generally I have found to be a very useful piece of kit, since it covers a wide range of devices, including testing many 74(LS) logic parts.
However, I have found it to be rather deficient when programming or simply reading the content of the 'old fashioned' UV EPROMS.
Recently I have been attempting to bring an old Paratronics Logic State Analysers back to life. It contains a large number of 2716 EPROMS, which have suffered some corrosion to the pins. As a check I decided to read the contents after careful cleaning, simply to check that the contents had not deteriorated over time. However, to my dismay, the TL866 seemed to show the contents had become corrupted. Not convinced this was the case, I put one EPROM in the Maplin SBC and read the contents via a MICE emulator. Surprise! The contents revealed now to be quite OK.
My conclusion is that the programmer timings for accessing such devices is far too quick; I may at some time 'scope the waveforms to confirm thgis. I have previously commented that the timing for Vpp on these devices is far too short, being a maximum given as 1ms, rather than the 40 - 50ms given in the datasheet.
So, here is another trap for young players, as Dave Jones might say.
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Old 6th Jul 2020, 10:32 am   #49
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Default Re: Maplin Z80 SBC

For nearly all EPROMs there is a slow / standard ''generic" algorithm which will work with any EPROM of that same general type (any 2732, any 2764, etc).

But, for nearly all EPROMs there is also a faster manufacturer specific programming algorithm. When you select device type 2764 / Manufacturer SGS-Thompson (for example) the programmer will use SGS-Thompson's fast programming algorithm.

That doesn't seem to be reliable for you so if your programmer has a manufacturer: 'Generic' setting use that, as that will make the programmer use the slow-but-sure basic programming algorithm.

-Reading- EPROMs too fast is a different issue, sounds like quite a bad design fault. I don't suppose you can alter the read speed in the menus somewhere?
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Old 6th Jul 2020, 4:27 pm   #50
mikew8760
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Question Re: Maplin Z80 SBC

Thanks for your observations. Unfortunately there are no options for changing any of the EPROM programming values; I suspect the design was made by a young chap (in China!) for whom devices like UV EPROMS were something he had read about in history books, but no practical hands-on experience. The difference between Vpp times, which are selectable from 50 us up to a maximum of 1000us, and data sheet values seems to be a glaring omission. Or perhaps I'm looking at the wrong data?
As regards your comment on EPROM reading, I'm wondering if there has been some kind of degradation of the silicon, thus changing the characteristics? Jerry Walker has commented in his videos that (74 series logic, etc.) can 'age' over time and become unreliable in some way. If I recollect correctly, data access time for a 2716 is 350 - 450ns. It seems unlikely that the programmer is defeating this time? The SBC would work since the Z80 is only running at 2MHz, but I shall be curious to try and check out the timings.
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Old 6th Jul 2020, 4:30 pm   #51
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Default Re: Maplin Z80 SBC

Is it possible the TL866 is trying to use the program verify mode of the 2716, but is unable to provide the 25v to select the mode correctly? I believe the TL866 is not able to generate 25v required for the older uveproms.

Another possibility is that the threshold of eproms internal detection of 0 or 1 is using a voltage reference based of the supply voltage. I have read in other forums that the data can sometimes be retrieved by lowering the supply voltage, but have not tried this myself yet.

I got myself a PRG-055 programmer last year, which is supposed to work with the higher voltage eproms but still haven’t got round to verifying this yet.

It’s possible that your eproms are becoming unreliable with fade of the programs, so it might be a good idea to dump the contents to files as backup. Try multiple reads and compare to make sure each read is the same.
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Old 6th Jul 2020, 5:45 pm   #52
philoupat83
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Default Re: Maplin Z80 SBC

hello
I have often used my TL866CS programmer upgraded to TL866a. It says 21v for some eprom.
by forcing several times the programming can program 25v eprom when I say several times it's many times without stopping and after x ten minutes by insisting the Eprom is programmed wow wow
there is an alternative scheme that I've successfully tested.
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Old 6th Jul 2020, 5:49 pm   #53
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Default Re: Maplin Z80 SBC

but lately I've been ordering a tl866II+ signed XGecu and it's not working.
always an overcurrent even with a test circuit ttl
radioman is no longer a match, so I'm looking for
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Old 6th Jul 2020, 5:49 pm   #54
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Default Re: Maplin Z80 SBC

the tl866II+ is only 18v maximum
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Old 6th Jul 2020, 6:13 pm   #55
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Default Re: Maplin Z80 SBC

Do these programmers actually claim compatibility with the 2716 or have them in their official device list? If so, someone is having a laugh.

In an emergency I seem to remember you can use 2732 or 27C32 or 2732A as a 2716 substitute by programming the code into the upper half of the 27..32 device, so if your programmer can supply the VPP needed by any of those devices that's one possible way to bypass the problem.

It still doesn't help you to read the code out from the original 2716s in the first place though.
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Old 6th Jul 2020, 8:42 pm   #56
philoupat83
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Default Re: Maplin Z80 SBC

the minipro tl866a reads the 2716 MBM2716 from fujitsu M2716 from ST TMS2716 from TI and others.
nevertheless to program vintage eprom I found a compact100 programmer that I'm repairing
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Old 6th Jul 2020, 9:20 pm   #57
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Default Re: Maplin Z80 SBC

I have a TL866II+ (XGecu) as well and I have been able to read out most EPROM's I throw at it. But I cannot program as you say anything that requires higher voltages. I have a number of ST2764A which are 8K ones that it can program as they are 12.5v. So far I have managed although I did struggle with my ZX80 kit as it needed a 4K part!
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Old 6th Jul 2020, 9:29 pm   #58
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Default Re: Maplin Z80 SBC

The minipro TL866A is the version before the TL866II+.
the alternative schematic works, you have to make a small card and have a 25V or 21V power supply.
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Old 6th Jul 2020, 9:36 pm   #59
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Default Re: Maplin Z80 SBC

I got a compact 100
minato 1866A with the notice it works I am going to interface it in USB it makes the 2516 and 2532 2716 2732 etc
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Old 7th Jul 2020, 10:11 am   #60
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Default Re: Maplin Z80 SBC

I have a TL866a and it programs the AMD 2716 chips I have. The problem with 2716 EPROMs is they came in many variants so it's important to select the right manufacturer from the device list and I wouldn't be at all surprised if some are not supported. Later devices generally are, early devices sometimes needed 27v programming and different algorithms that aren't supported. It might be easier to get 2816 flash EEPROMs and use those for that "mask programmed" ROM look!
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