Lpc2000

Chaps,

I'd like to pick your collective brains.

I'm using a 2194 that communicates with lots of other devices using all 
four CAN ports and both UARTs. One UART communicates with an AVR which 
does some real time stuff and passes data to the ARM, and the other 
talks to a PC. I need to add another UART, which means I need to somehow 
free up the serial port that talks to the AVR and come up with an 
alternative way of getting the two devices to communicate.

I would do it as a parallel interface using P1 if it wasn't for the 
ridiculous pinout of that port! The next best way seems like it might be 
SPI (as I'm not using the SPI port). I would almost definitely have to 
go to four layer if I did it this way, and I don't want to do that.

Would I be mad to try this? It strikes me from reading about various SPI 
issues on here I might be asking for trouble. I need to get information 
out of the AVR and into the ARM as rapidly as possible and also get 
configuration data from the ARM to the AVR, so I'm assuming I would have 
to change which was master and slave from time to time?

I would add I've done lots of SPI in the past, but always with the micro 
being the master and talking to D/As, EEPROMs etc. I'm wondering how 
difficult it is to get a micro running as a slave, and in particular the 
2194, as my perception is the LPC family has some SPI issues. (This may 
well be a false impression of course.)

I have thought about using an SPI UART, but I think only Maxim do those 
and I refuse to use Maxim stuff!

Many thanks,

Rob