The pinout differences between the 27C256 and 28C256 are:

27C256 pin 1  = VPP  28C256 pin 1  = A14
27C256 pin 27 = A14  28C256 pin 27 = /WE

Paul

> -----Original Message-----
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Justin Grimm
> Sent: Wednesday, November 27, 2002 8:42 PM
<snip>
>
> When changing from a 27256 to a 28256 all the data and address
> lines are the
> same aren't they? The only difference should be the programming pin?
>
> The application is a siemens s5 programming unit (simatic pg740)(simatic
> plc). We only have eprom memory cards and we require eeprom
> memory cards but
> they're too expensive. I would like to replace the eprom with the
> eeprom but
> I don't know if it's ok to do.
>
> The cards look universal and have a spare slot next to the eprom
> slot- maybe
> they're for an eeprom.
>
> Is anyone familiar with these memory cards?
>
> Justin

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