Blackfin CAN Pin operation after power-on

Document created by analog-archivist Employee on Feb 23, 2016
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There is a statement in the Hardware Reference Manual that suggests that the
output state on the CANTX pin may be low if the muxed pin is configured as a
SPORT pin, which is the default state after reset.  Since logic low is dominant
on the CAN bus, won't this always corrupt the CAN bus when the Blackfin starts
up?

 

This would only be an issue if the function enable register (PORT_FER) is
configured such that the CANTX and CANRX pins are being utilized as peripheral
pins rather than as GPIO pins before the port multiplex register (PORT_MUX) is
written to configure them as CAN pins instead of as SPORT pins.  After reset,
the PORT_FER register defaults to all pins being GPIO, which means there is
nothing driven on those pins.  As long as the PORT_MUX register is configured
for CAN use (by setting PJCE to b#01) before PORT_FER is written to have those
pins function as peripheral pins, there will not be a case where you are
driving dominant on CANTX due to misconfigured pins.

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