Adrian, I have a couple of 16C74A projects that use external SRAM with
built-in Clock/Calendars. Check out Dallas Semiconductor products if you
are interested in combined SRAM, RTCC, Crystal, and Battery. I use Port E
and D as you described. In one project I use a 512KByte Dallas SRAM/RTCC
with an external address decoder and address latches. In another I use a
version that multiplexes the address and data lines. They have several
such devices. In addition to RD/WR/CS, you need ALE (Address Latch Enable)
and upper/lower address strobe inputs. You can get them with or without
internal clocks and batteries.

   - Tom

At 06:24 AM 3/3/98 -0500, you wrote:
>I intend to interface an SRAM using 3 or 4 bits of Port A (RA0,1,2,5) as
>A15:17, RC0:5 as A8:15, Port D as D0:7, and RE0:3 for CS, OE, and WR.
>
>The first lash-up will use a 6116, moving on to the biggest SRAM for which
>I have enough i/o lines. It'll be battery backed.
>
>I've half-seriously considered serial-flash but don't want to suffer the
>erase time periodically since RS232 data is coming in on other Port A bits
>(software UART) and going out on RC6:7 (hardware UART) most of the time.
>
>Has anyone done something similar before?
>Comments?
>
>Regards
>
>Adrian
>
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