Joshua Woods wrote:
> 
> Thanks for that info.
> 
> If I went with option a):
> to make up the 32kx16, would I connect A[0..15] in parallel with each device,
and then AD[0.7] to the first device and AD[8..15] to the second
device?  With
FLASH chip select going to both CHIP devices.??
> 

Do it somehow like the following schematic:

       +-------------------+
       |            ALE    |
       |                   |
+----------+ AD[0..15] +------+  A[0..15]
| 17C4x    |===========| '573 |============     
|          |       #   +------+           #
+----------+       #                      #
                   #      +----+ A0..14   #
                   # D0..7|    |==========#
                   #======|    |          #
                   #      |RAM |          #
                   #      |    |          #
                   #      +----+          #
                   #                      #
                   #      +----+ A0..14   #
                   #D8..15|    |==========#
                   #======|    |          #
                          |RAM |
                          |    |
                          +----+

Then use A15, /OE and /RD to select the RAMs in the correct
address space.

CAVEAT!
When you want to change single bytes (not 16bit words) in your RAM,
then remember first to read both bytes, modify one and write them
back.
Note, there is a bug (feature?)  - at least in the 17C44 I worked with -
which I sent to the group some time ago:

==========
There is a discrepancy between manual/simulator and real 17C44,
concerning the Table-Latch TABLATH/TABLATL.
I want to write single bytes into external 16-Bit RAM, connected to
a 17C44 in microprocessor mode. If you read the manual, you should
think,
the following code sequence is correct:


        (set tablptrl and tablptrh)
        tablrd  0,0,wreg                ; dummy read to fill TABLAT with
16 Bit
        tablwt  0,0,myvalue             ; write low-byte, store both
bytes

The simulator of MPLAB also agrees with this code fragment, BUT NOT the
17C44!

For real world, I need the following code fragment:

        (set tablptrl and tablptrh)
        tablrd  0,0,wreg                ; dummy read to fill TABLAT
        tlrd    1,wreg                  ; read high-byte from TABLATH
        tlwt    1,wreg                  ; write high-byte to TABLATH
        tablwt  0,0,myvalue             ; write low-byte, store both
bytes

Well, it took me 2 days to find out! I always thought, my hardware was
bad.

What does Microchip think about this?
How behave the other PIC17Cxx ?
==========

Unfortunately, I never received an answer from Microchip concerning
this fact.

Regards,

Wolfram

-- 

+------------------------------------------------+
! Wolfram Liebchen, Forschungsinstitut fŸr Optik !
! mailto:liebchen@ffo.fgan.de                    !
+------------------------------------------------+