Hi Stefan
Sorry I didn't get back to you. Things got busy and
I've been away from the net over the weekend. It looks
like you need to make an adapter to at least disconnect
Pin 22 so the VPP level can't get to the chips pin.
The mask ROMs may have any of the 4 configurations for
pins 20 and 22. I would try first just disconnecting
22 from the test side and connecting the chips pin
22 to pin 20. This assumes that the mask ROM uses the same
selects as the EPROM does. I'd do that as the first try.
Does anyone remember which pin they pull high on to
check the manufacture ID. I think it was A11 but I'm not
all that sure. It would be a good Idea to stack two
resistors of about 1K in series with this lead. One
should place a diode to VCC ( pin 28 ) to the junction
of the two resistors with the band towards VCC. This
will protect the part against any ID test voltage that
might be used. It would still allow the address to pass.
Dwight
>From: birs23_at_zeelandnet.nl
>
>You can find that here :
>http://www.xs4all.nl/~ganswijk/chipdir/holtek/ht23c256.txt
>
>For a 27256 you can look here :
>http://www.xs4all.nl/~ganswijk/chipdir/giicm/27512.txt
>
>Cheers,
>
>Stefan
>
>At 23:09 22-10-2004, you wrote:
>>Hi
>> I guess the next thing is to find a pinout for
>>the 23512 to see if they have a select that is inverted
>>that might need to be patched around to read on
>>a standard programmer.
>>Dwight
>>
>> >From: birs23_at_zeelandnet.nl
>> >
>> >Dwight, not missing the discussion ;-)
>> >
>> >At 19:15 22-10-2004, you wrote:
>> >
>> >> >From: ard_at_p850ug1.demon.co.uk
>> >> >
>> >> >>
>> >> >> Hi,
>> >> >>
>> >> >> I know very little about electronics and eproms so this question
>> might be
>> >> >> really easy. I would like to know what the difference is between a
>> 23512
>> >> >> eprom and a 27512 and if there are any differences if its possible to
>> >> make
>> >> >
>> >> >I thought the 23512 was the mask-programmed part (not an EPROM), and is
>> >> >otherwise the same device. You should be able to read it (unless your
>> >> >programmer tries to be clever and read the manufacturer's ID word, etc).
>> >> >
>> >> >-tony
>> >> >
>> >>
>> >>Hi Tony
>> >> I think you are right about the 23xxx being mask versions.
>> >>The problem with the newer EPROM parts is that they do not
>> >>require pulsing of the programming voltage. Many programmers
>> >>simply leave the programming voltage high while reading or
>> >>verifying. This is real bad for mask parts. Also, most mask
>> >>parts use the programming voltage pin as another select.
>> >>This means that it may need to be in the opposite state that,
>> >>even a programmer that allows setting of the program voltage,
>> >>may not be in the right state to read.
>> >> Also, I think this fellow is off the list and doesn't realize
>> >>that he is talking to a list. I suspect he is missing our
>> >>conversations related to his issue.
>> >>Dwight
>> >
>> >
>
>
Received on Mon Oct 25 2004 - 11:14:09 BST