8-bit and 32-bit external memory devices with MPC555

Hello,

We're a little confused about external memory accesses using the
MPC555 and are hoping someone can set us straight. We're using a
DS3832 static RAM in our design. This chip really contains two
separate physical devices, a 32-bit RAM and an 8-bit RTC. The RTC has
its own 8 data pins separate from the 32 RAM data pins and its own
/CE, /WE, and /OE pins separate from those of the RAM.

For the 32-bit RAM, MPC555 signals DATA[0:31] are connected to the
RAM's 32 data pins, with MPC555 DATA[31] connected to RAM D0, MPC555
DATA[30] connected to RAM D1, etc. We are using MPC555 CS1 for chip
enable of all 4 RAM bytes and WE[0:3] for write enable.

For the 8-bit RAM, MPC555 signals DATA[0:7] are connected to the RTC's
8 data pins, with MPC555 DATA[7] connected to RTC D0, MPC555 DATA[6]
connected to RTC D1, etc. We are using MPC555 CS2 for chip enable of
the RTC and WE[0] for write enable.

Can someone confirm that we're doing this correctly? It's strange that
the 8 MPC555 data lines and the WE signal used for an 8-bit device are
not the ones associated with the least-significant byte of the 32-bit
device.

Thanks for your help.

Joe Pasquariello 







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