On Wed, Mar 11, 2009 at 08:11:32AM -0400, Roger Weichert wrote:
> Hi guys,  I have a need to program a number of M27C256B Eproms and have 
> spent some time searching old posts to work out what I should purchase.
> 
> At this stage I don't envisage doing much else with it, just this particular 
> eprom . and probably only a few a month.
> 
> I need to be able to copy a master chip, then reprogram several others with 
> the updated software.
> 
> Does anyone have any advice on the best device for the job please?

Depending on the time you have available you could build a one off
programmer fairly easily. Looking at the data sheet:

http://www.st.com/stonline/products/literature/ds/2384.pdf

Programming is done by applying a 6.25V supply to Vcc and a 12.75V supply
to Vpp. I would create a programmable power supply by using the old Steve Ciarcia 
trick of using a LM317 variable regulator and digitally switch in different
valued resistors to change the voltage. Here's an old post of mine that
describes it:

http://www.nabble.com/-PIC--Best-way-to-program-a-OTP-EPROM-PIC-td2649189.html

"...A high current switchable Vpp is pretty easy to put together using a
LM317 and a couple of transistors. Use one transistor to ground the ADJ pin
and a second to ground OUT after passing through a current limiting
resistor. When both transistors are switched on, the 1.25V output of the
LM317 is shunted via the out transistor. When both are off the ADJ pin
rises to normal voltage divider setting of 13V. If the current limiting
resistor is 100 ohms, then 130mA of current is available to drive Vpp.

This is an old Steve Ciarcia design that he used for an intelligent EPROM
programmer."

Take a look at the brief LM317 description here:

http://www.circuit-innovations.co.uk/LM317.html

If you put a switch between the bottom leg of R2 and ground and add
multiple R2 (each switched) then you can change the voltage. IIRC he used
7407 OC buffers. But a NPN transistor will work just as well too.

Given that circuit, the rest is pretty simple. A 40 pin PIC with PORTB
wired directly to the data lines, PORTD used to select the address using an
external 74HC573 as a page latch (also wired to PORTD), and some set of
ports A,C, and E pins to control the control lines, voltage switches, and latch
would lash up a suitable EPROM programmer/copier pretty easily. The only
other addition would probably be a SPI/I2C FRAM hooked up to the syncronous
serial interface to hold the contents of the EPROM you are copying. Add a
couple of buttons and an LED, and call it a day. 3 chips and a handful of
components along with a 15V input supply is all that you'd need to make it
work.

Hope this gives you some ideas.

BAJ
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