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Re: old magazine article -- interesting ! ??

Posted: Tue Jan 16, 2018 11:48 pm
by gammaray
I ordered the article. It costs $5 would have been cheaper (free) when I worked at UTArlington.

We will see in a few days if it is out there.

Charles

Re: old magazine article -- interesting ! ??

Posted: Wed Jan 17, 2018 6:44 pm
by gammaray
Having to ask librarian to check again as they sent me Jan not Feb

Does anybody know if Computer Digest was monthly or quarterly or bi monthly?

Re: old magazine article -- interesting ! ??

Posted: Wed Jan 17, 2018 9:51 pm
by gammaray
Here it is ... in MARCH!
298716.pdf
(534.77 KiB) Downloaded 111 times

Re: old magazine article -- interesting ! ??

Posted: Wed Jan 17, 2018 10:42 pm
by mrtinb
It seems building this unit is useless unless someone has the content of the EPROM Operation System Software sold from the magazine.

Re: old magazine article -- interesting ! ??

Posted: Thu Jan 18, 2018 12:00 am
by gammaray
Great reverse engineering project... company is Wildonics.

WILDONICS, Box 1763, Boise, ID 83701

Nothing current online.

Re: old magazine article -- interesting ! ??

Posted: Wed Mar 13, 2019 1:29 pm
by jdfan1000
Reviving this after a year. Mark Latham is on Facebook. I've reached out to him through it.

Re: old magazine article -- interesting ! ??

Posted: Mon May 13, 2019 12:38 am
by 2late
mrtinb wrote:
Wed Jan 17, 2018 10:42 pm
It seems building this unit is useless unless someone has the content of the EPROM Operation System Software sold from the magazine.
I built such a thing, also using a 8255, because they where easier to program and cheap as sh*t compared to the fancy Z80PIO. EPROM-programming software is trivial. You put the address, you want to program into to the address pins and the contents to the data pins and then you pulse the programming pin. The exact nature of this pulse is described in the application sheet of the EPROM. I remember having done 2708, 2716 and 2732. The 2708 is rather complicated, even while in normal use. It is not content with +5V, but also needs -5V and 12V just to be read. You also need this voltages for programming. In addition you need high voltage pulses for the programming. So you need an amplifier to produce this voltage out of your 5V programming signal. You need to do about 100 pulses with a pause after each one so that you don't broil this one 8bit storage location. You can speed up programming by going through the address in the inner loop and the 100 pulses in the outer loop, but to be on the sure side it still took hours to get 1k into that chip.

It is much simpler with the 2716 and beyond. The are content with 5V. Only for programming you need a higher voltage, but this can be constant. The programming puls is a simple 5V signal directly out of one of the ports of the 8255. The amplifier seems to be integrated. You had to use fast mode of course to get the timing right.

What is new to me is that you could use IOREQ. I remember having read that a ZX81 was likely to crash on any IO-operation so I crammed the 8255 and everything else for that matter into the $2000 to $3FFF space with the help of one or more 74LS138.