Hello All.

I have a question regarding the SPI and I2C synchronous comm standards.
In a design I am currently working on, I have managed to get my PIC
(17C756) to successfully communicate with an MX803A audio tone
generation IC via the SPI using the MPLAB C-17 SPI libraries.  My
design, though, also requires at least 32kbytes of EEPROM.  Since, as I
understand it, SPI will require a separate CS for every device on the
bus, I am looking for a less I/O intensive approach.  I see three
possible scenarios:

Scenario 1:  Use I2C for all comms.  This is the best choice since I2C
does not require CS.  The only problem here is that I don't know if
there is a way make an SPI device respond to I2C addressing.

Scenario 2:  Use SPI for all comm.  I need 32kbytes of memory; since
this will require 4 each 64kbit EEPROMs (microchip p/n 25LC640), then it
looks like I will have to use 5 separate I/O lines for chip selects, 1
for my tone generator and 4 for the EEPROMs.  The quantity of I/O I have
to use for CS in this scenario is high, close to unacceptable.

Scenario 3:  Use SPI for the tone generator, and I2C for the EEPROMs.
This will only work if the 17C756 will support both SPI and I2C modes
simultaneously, and I do not know if it will.

Well, that's it.  Any suggestions?



+++++++++++++++++++++++++++++++++++++++
++      Dan Tye
++      Chief Engineer
++      Tel-Tron Technologies Corporation
++      220 Fentress Boulevard
++      Daytona Beach, FL 32114
++      Phone: 904-255-1921    Fax: 904-258-3782
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