🚀 go-pugleaf

From: Bill Witts <william@uk.ac.ucl.cs>


I am designing an EPROM programmer.  It should deal with
27C64/128/256, and any other devices that are easily
accommodated.  I have figured out the following algorithm,
based on knowledge and intuition in roughly equal portions:

1.      Apply Address,Data, /OE = /CS = 5v, Vpp = 0v, Vcc = 5v,
        (/PGM = 0v)
2.      Apply Vpp = 12.5 and wait 1ms
3.      Apply Vpp = 0v, remove Data, and set /OE=/CS=0v.
4.      If Data is not correct, then go to 2 until fed up - error!
5.      If data OK, then goto 1 until ROM is finished.

Questions:
a)      Do you need to select the chip before it will program?
        Eg. Should /CS=0v in step 1?  Are there any glaring
        errors in the alg?
b)      I have always strapped Vpp to 5v in the past during
        normal operation due to ancient advice. Is this
        necessary, or will a ROM work normally with Vpp = 0v?
c)      Other EPROM programmers seem to protect themselves
        against ROMs being put in upsidedown, and to detect bad
        ROMS.  How do you detect the former, and can the latter
        be detected before putting Vpp = 12.5v?  I hate the
        idea of all the sensitive electronics being fried!  I
        plan to put a crowbar diode protection on all the
        signal lines on the ROM to prevent overvoltage >5.6V - is
        this necessary/sufficient?
d)      I also have 21v available.  Would this algorithm work
        OK on ROMs accepting this voltage, in general?
e)      What is the maximum operating current drawn by the Vpp
        pin during programming?

I have a few ideas on these points, but info seems scarce
hereabouts, and nobody I know seems to really know anything
about the details.  If I had a ROM programmer to hand I would
like to experiment, but I haven't - that's why I am building
one!

Many thanks in advance,  e-mail replies, I will summarize if this
seems to catch the public imagination!

                        ... Bill

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Bill Witts, CS Dept.     *    Nel Mezzo del cammin di nostra vita
UCL, London, Errrp       *    mi ritrovai per una selva oscura
william@cs.ucl.ac.uk     *    che la diritta via era smarrita.
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