[Coco] Re: EPROM eraser wanted

[Stephen H. Fischer]

Hi,

Gene Heskett wrote:
>> You can convince many people that a simple task is one that requires
>> huge $$$$.
>>
>> For the limited number of EPROM types that CoCo'ers would want to
>> program the parts cost is trivial.
>>
>> Five dollars is too much I suspect even today if the very old parts
>> have not risen in price. Using today's parts, it may be a simple one
>> chip solution (PIC).
>>
>> While I have not constructed (As far as I remember) the simple
>> programmer that I determined would be all that is necessary and I
>> have not written the software I can supply the basis of that
>> conclusion (A more parts intensive burner that I have and used
>> several times for the SYM-1). Both the hardware and software needed
>> is very simple once you understand the simple task. The CoCo is
>> better for the task than a PC and if I remember correctly, I planned
>> to write the software in BASIC.
>
> Mine had to interface with a z80 board with an ss50 buss IIRC, and had 3
> latches to hold the address and data during the write pulse, and a
> timer to control the pulse duration, read-write operations being
> switched by turning an lm317 up and down to get the write voltage, then
> 25 volts but soon lowered to 17 volts by newer chips coming online.
>
> Write pulse duration was set by the timer, the timer being triggered by
> the write strobe to the data latch with a couple of gates to delay so
> the data was well setup by the time the lm317 went up. IIRC that put a
> hold on the z-80 until the write pulse was over, at which point my
> software did a trial read to see if the data was good, if it was then
> it shifted the count of how many pulses it had taken to get that good
> read, and did half that many more write pulses blind as recommended by
> the chip people at the time. The it went on to the next address and
> repeated the routine.
>
> And from that you should be able to build a burner. I remember one
> gotcha with the z-80, if all other access sigs were valid except the
> read, then it was going to be a write, since the z-80's write pulse was
> considerably delayed compared to its read pulse, so those conditions
> were then used to preset the burner for an upcoming write operation.
> The write pulse itself was then ignored.
>
>> --
>> Stephen H. Fischer
>
> --
> Cheers, Gene

Yep, that's some of the thoughts that I had along with some features
eliminated like no power switch, the higher power applied by connecting a
wire from my bench power supply with a alligator clip when needed.
I remember now that I got as far as to put, not a zif socket but a burn in
type, socket for the EPROM on a board which socket I remember cost very
little when compared to a ZIF.

The basic task is you need to set the address lines, data lines and then
apply higher voltage to a pin and then a pulse to another pin (Your mileage
may vary, some of the earlier EPROM's were very unfriendly to program).

I planned to use serial to parallel converters for setting the address and
data lines to reduce the number of pins used on the SYM-1 burner. Maybe even
a ripple counter as only full burning was planned.

The SYM-1 board has many PIA's and thus a huge number of pins that can be
used to control off board devices. It just was too much work to connect them
all. When EPROMS got larger, adding more address lines suggested to me that
it was time for a new design.

Should anyone want to build an EPROM burner for the CoCo we could discuss
this more and generate a minimal parts board. I would look for the start I
did if it has not gotten lost for the prototype.

Stephen H. Fischer