Hi - I'm looking at using an MCP2515 in an upcoming circuit. It seems fairly straightforward - but there's one little thing I'm worried about. I'm planning on using an ATMEGA48. I'm running pretty low on GPIOs so I figured I could connect a 20mhz crystal to the MCP2515 and then use its CLKOUT pin to drive XTAL1 on the ATMEGA48. I plan on programming the ATMEGA48 both initially and periodically with an AVRISP (I'm sure glad I have a spare now that they're no longer made!!!). Also - the MCP2515 and the AVRISP will be sharing the SPI, so I understand I need resistors inline with the MCP2515. I was thinking I'd just put 1Ks there to start with and see if that worked ok. Any idea how to calculate the value for that resistor?
Anybody see any problems with this plan? I need to be able to do both the initial and final programming on this board (as the ATMEGA48 is a TQFP).