RE: 1541 ROMs question

From: Baltissen, R (Ruud) (
Date: 2001-12-19 07:32:40

Hallo William,

> A logic probe would be safer.  You would not be able to measure the
> voltage, but you should be able to tell which is the program pin.

What good is to know which pin is the program pin if you don't know where to
apply the 25 V to?

We have 24 pins:
1- 13 addresslines
2- 8 datalines
3- Vss = GND
4- Vcc
5- ChipSelect

We can scratch 1 to 3 as possible candidates for the 25 V.
Choosing pin 24 = Vcc for the 25 V means the 68764 needs an internal 5V
regulator for supplying power to the rest of the IC not able to cope with
the 25 V. Think of the heat generated using this construction.
I favour the CS-pin, both as Vpp and program pin: apply 25 V the moment the
address and data is valid. This also would mean that, when using an ordinary
voltmeter, we would not measure 25 V but maybe something like 10 V. Using a
scope would be better in this case.

> A logic probe would be safer.

Yes, for the EPROM and the prommer. But can the probe handle 25 V? :)
   / __|__
  / /  |_/     Groetjes, Ruud
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