To the group:

Has anyone in the group tried to interface a DRAM or multiple DRAMs with
the PIC product?  The one that I have in mind (for the PIC) is the
16F84, by virtue of the fact that right now it is the only one I have
available to me.  The DRAM in question is a LH21256Z-10 manufactured by
Sharp.  It is a page-mode operation part with 262144 words by 1 bit in a
16 pin dip.

All I am trying to do is come up with some rudimentary way of
communicating and reading/writing/testing one of this type of part at a
time.  The reason is this:  There are a number of these that are being
used in a weather monitoring application (used in a Motorola
68000/68010, 10MHz microprocessor card).  There are 16 of these used per
board.  After being in the field for a while, some as short as a few
months in the field, some as long as two years, there is a failure when
an attempt is made to boot up the system.  The machine displays a "RAM
failure" during the boot sequence, mentioning an address where the
failure occurred.  The failure rate is relatively low, but the customer
is concerned nonetheless.

The customer has led me to believe that -- at the specific address where
failure is alleged to occur -- that there must be some change in
parametric data.  I am wondering if I could use the 16F84 to write to
this part, do the refreshes, and then somehow do some sort of readback
or other technique to see if any of the data has changed.

Any ideas are welcome.

K. Schauf


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