21MX proms (per request

dwight dkelvey at hotmail.com
Thu Sep 10 13:19:54 CDT 2015

> From: ard at p850ug1.demon.co.uk
> To: cctalk at classiccmp.org
> Subject: RE: 21MX proms (per request
> Date: Thu, 10 Sep 2015 14:14:44 +0000
> > 2716 are that last of the program by turning the programming voltage
> > on and off.
> I must be mis-remembering how I designed my first EPROM programmer. I 
> know I could do 2716s (single-rail, not the TI ones) and I thought I always 
> applied Vpp and pulsed another pin at TTL levels to program them
> IIRC the 27128 was the last one to actually allow the 'dumb' 50ms
> programming algorithm. It may well work on larger chips, but 
> I never tried it.  That's why I designed my programmer to do
> 2716s, 2732s, 2764s and 27128s only. Not having another 
> programmer I couldn't use a microprocessor or microcontroller
> (no way to load the firmware) so I had to do it all in TTL logic. 
> Doing the 'intellegent' algorithm in TTL was a bit much ;-)
> -tony

Your right, I didn't say that the 2716 was not a single rail, just that it
didn't have a separate Vpp and PGM pin. It was programmed by turning
Vpp on and off. I could be wrong that the 2732s were that way as well.
The TI 2716s were not so friendly.
Intel sold half bad 2716s for 5 volt 2508s. Even after 2716s price dropped,
they still sold 2708s for $32 when you could buy a 2716 for $3 to $4.


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