On Thu, 13 May 1999 03:25:54 +0000, you wrote:

>Want a recommendation for a serial EEPROM or other non-volatile memory
>in the 256k to 4Mb range to which a 12C509 may speak.
>
>Constraints:
>        - eight pin dip,
>        - 5v supply,
>        - small quantities (10-50).
>
>For an antique computer, an 80C85 based Tandy 100/102/200 laptop, I have
>volunteered to a group of users on the 'net to investigate the
>construction of a simple device to act as offline storage.
>
>I had envisaged a 12C509 talking to a serial EEPROM.
>
>The interface to the laptop would be via the RS-232-like serial port,
>which I can program under software control to all sorts of baud rates.
>An 81C55 timer is used as the baud rate source.
>
>Ideally I'd want to fit the two chips into a DB25 backshell; though they
>are getting small nowadays, these backshells.
>
>I expect to run the device from power available from the DB25 socket,
>i.e. parasitic with "shocking" diodes, now that I understand why.  ;-)
You might consider using a larger PIC to control an external
battery-backed parallel SRAM, or flash device - probably no more
expensive, rather larger but should fit a D25 'dongle' box.