jgb@prism.gatech.EDU (James G. Baker) (11/15/90)
I was hoping to make a PROM programmer. Of course, the reading of this
27C256 is no problem, programming it is much different from TTL. If I wish
to have the programming voltage (13 volts) and the Vcc=6.5 under software
control, could I use a Digital-to-Analog converter and some bodacious OpAmp
circuit to do this?
Here are the specs:
Signal READ PROGRAM
Vcc +5.0 +6.5
Vpp +5.0 +13.5 (30mA)
Can I skimp at all with these voltages specs? I am using a PC interface with
Gnd, +5, -5, +12, and -12. Any help would be most appreciated.
Respond via e-mail to jgb@prism.gatech.edu
Thanks!
--
BAKER,JAMES G - Lab Technician, School of Electrical Engineering
Georgia Institute of Technology, Atlanta Georgia, 30332
uucp: ...!{decvax,hplabs,ncar,purdue,rutgers}!gatech!prism!jgb
Internet: jgb@prism.gatech.edujimc@isc-br.ISC-BR.COM (Jim Cathey) (11/16/90)
In article <17095@hydra.gatech.EDU> jgb@prism.gatech.EDU (James G. Baker) writes: >I was hoping to make a PROM programmer. Of course, the reading of this >27C256 is no problem, programming it is much different from TTL. If I wish >to have the programming voltage (13 volts) and the Vcc=6.5 under software >control, could I use a Digital-to-Analog converter and some bodacious OpAmp >circuit to do this? > >Here are the specs: > Signal READ PROGRAM > Vcc +5.0 +6.5 > Vpp +5.0 +13.5 (30mA) > >Can I skimp at all with these voltages specs? I am using a PC interface with >Gnd, +5, -5, +12, and -12. Any help would be most appreciated. No, you can't skimp. Won't program correctly if you do (early Alzheimers, etc.) What I did when I built mine was to take a LM317 variable voltage regulator (two, actually -- one for Vcc and one for Vpp) and connect a resistor chain in place of the single resistor shown in the bottom place of the typical schematic. I then took several 7407 (high voltage open collector buffers) gates and tied the outputs to the various tap points. Grounding taps higher and higher on the chain by driving the proper gate input high results in lower voltages on the output. Resistors sized to produce the proper voltages. Resistors were actually a bunch of small PCB pots on my prototype, the production unit would have had properly sized 1% resistors. (There never was a production unit -- they didn't want one after all.) The Vcc regulator was powered from +8VDC off the S-100 bus, the Vpp regulator (which has to go to 24V or so for some parts) I got from a voltage doubler that used a medium power transistor, the +16V supply, and the system clock to drive it -- as I recall I got between 28 and 30 volts out of it. Some tinkering with a similar scheme (probably a tripler) would work here. A little bit of heat sinking, some TTL latches for the data/address/control lines, and a DIP header for Vpp line rearrangement and I was all set. Mine was supposed to go from 2716 (single voltage type) on up to 27256, which was the biggest in the wings at the time. Should have had no real limits on it. I never tested anything larger than a 2764, though. Oh, I think that some PROMs have lines that have to switch from Vpp to ground during verify or something. I accomplished this with a PNP series pass transistor feeding the LM317 and another 7407 clamp on the output of the voltage regulator. This was definitely the ugliest part of the job, quite the hack really. Careful phasing of the control lines on the regulators is necessary, the logic should be make-before-break on the chain taps to prevent high-voltage glitches, and for obvious reasons you have to make sure the pass transistor and the output clamp are never on together. A small decoupling cap on the chain doesn't hurt. I had almost no output capacitance on the regulators so they could switch voltages quickly. It all seemed to work just fine, by the way. This was all in '83 or so. +----------------+ ! II CCCCCC ! Jim Cathey ! II SSSSCC ! ISC-Bunker Ramo ! II CC ! TAF-C8; Spokane, WA 99220 ! IISSSS CC ! UUCP: uunet!isc-br!jimc (jimc@isc-br.isc-br.com) ! II CCCCCC ! (509) 927-5757 +----------------+ "With excitement like this, who is needing enemas?"