The only other thing to be aware of is to use ADDR [31..xx] for the 8 bit
device and ADDR [29..xx] for the 32 bit device. Table 10-4 on page 10-21
illustrates this but doesn't exactly explain it in detail. It might be some
other place in the manual as well but I don't remember off the top of my
head.
Tom
> -----Original Message-----
> From: trailrunner23 [mailto:[email protected]]
> Sent: Wednesday, July 20, 2005 1:04 PM
> To: [email protected]
> Subject: [MPC500] 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
>
>
>
>
>
>
>
> -----------------------------------------------------------
> To learn more about Freescale Microcontrollers, please visit
> http://www.freescale.com/mcu
>
>
>
> Yahoo! Groups Links
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>
>
>
>
>
>
>
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