Old EPROM questions again, EPROM Programmer

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Thu Jul 29 18:35:28 2004

>
> >> Parts might be a bit hard to find now - uses a 6809 CPU, 6821 PIA, a 6551
> >> UART, a few 6264 SRAM's, a handful of latches and 3-4 relays to move the
>
> >And thereing lies the problem. Presumably you need to program an EPROM
> >with the firmware for this 6809. Which is somewhat hard without a
> >programmer :-)...
>
> For some perhaps - at the time, myself, and almost everyone I knew worked
> for companies with programmers, so it was not a problem. You could also get

You were lucky. I was a student at the time, and in fact I built the
program over an Easter vacation one year. I didn't have access to a
programmer -- that's why i needed to build one.

> EPROM programmed at the local shop for a small fee. I also had a bytesaver

There were mail-order companies who would do this in the UK, but they
charged qyite a bit for doing it (especially if they had to type in a
listing). At the time I didn't have a machine that wrote any form of
'standard' floppy disks (i.e. I didn't have an IBM PC).

Unless your programming skills are perfect (and mine are not), this gets
boring fast when you have to wait a few days for each update. In fact the
time taken to erase and reporgram an EPROM yourself soon becomes painful,
that's why I included an emulator in my programmer.

> in my Altair, so I could have bootstrapped up from a 2708 if I'd had to.
>
> I didn't program the actual firmware right away - I made a EPROM (at work)
> with my 6809 monitor program in it, which allowed me to download code into

Right... Again this assumes your monitor is debugged.

Incidentally, I've built a couple of instruments with microprocessors (as
opossed to microcontrollers) controlling them (actually I normally used
the 6809 -- nice chip), and I included commands to read/write/execute
from any location in mmeory. Sure helped debugging !.

> the RAM (normally all used as a data buffer), where I tested and debugged
> the actual firmware - When I was happy that everything was working correctly,
> I use the RAM download to program a real EPROM (almost self-booting).

Neat.

>
> If I were doing the same project today, and had absolutely no access to any
> means of programming the initial EPROM, I would first post in the local groups

These days I'd either use a PIC as the controller processor (trivial to
make a programmer for, and the programming algorithms are documented), or
if I was using some deviec with external program memory, I'd start off
using E2PROM or something, again easy to make a programmer for. I now
have access to rather more computers, with rather more user I/O lines...

> to see if anyone near me has a programmer, failing that, I would perhaps try

This was long before the days of the Internet in the UK. It wasn't easy to
find places to ask about borrowing a programmer.

> this list or other more widespread resources - I'm sure that someone somewhere
> would be willing to program my monitor (or even a very simple loader would

These days it's easy. I have a dozen programmers, and could build another
one in an afternoon without even thinking about it. And there are people
on this list who'd burn an EPROM from an Intel-hex file e-mailed to them.
This was not the case 18 years ago.

> suffice) into that first EPROM for me. All you need is the ability to get code
> into the device, and you can run from there.
>
> I guess what I am saying, is that if you are not prepared to be a little
> creative, you are probably not well suited to designing/building your own
> test equipment.

Are you saying I'm not creative? Heck, I got round the problems and built
a working programmer. I guess I should tell you how I verified the
program pulse width without an accurate counter. I used a TTL monostable
to generate the 50ms pulse, you see. I connected the input to a known
clock frequency (about 5Hz IIRC), divided down from an Xtal. The output
went to a buffer which I'd measured the output voltages (high and low)
for under static conditions. When the whole lot was patched together, I
measured the average output voltage using an analogue meter. From that I
could calculate the mark/space ratio. And thus the pulse width (knowing
the repition frequency). Worked well enough to program quite a few EPROMs...

>
>
>
> >I built my first EPROM programmer about 18 years ago. Programs
> >2716-27128, using the 'slow' algorithm. It doesn't even handle 12.5V
> >parts (I should add that feature!). 3 hand-wired boards of mostly TTL,
> >with a 40 pin AY-3-1015 UART in the middle. Oh yes, it's an EPROM
> >emulator as well, for the same types of EPROMs.
>
> On my original programmer (the homebuilt one), the programming voltage
> was selected by a physical switch - which selected 12.5, 21 or 25v from

Mine too. I just had a 2 position switch to select between 25V and 21V
for 2732s. 2716s always wer e25V, 2764s and 27128s were 21V. I should
sometime add a 12.5V regulator and use the other pole of the switch to
select between 21V and 12.5V for the 2764/27128 devices.

-tony
Received on Thu Jul 29 2004 - 18:35:28 BST