bus-fight on PE4 with rabbit 2000/BL1810

Dear Rabbit Forums:

I am working on a class project with the Rabbit 2000 and BL1810 prototyping board. We have written an ISR and are able to setup the Rabbit to trigger this ISR when we very explicitly drive PE4 high by momentarily jumpering it to Vcc. However, when we try to use an I/O pin to do the same, we can’t bring the voltage above about 0.6v. We’ve tried driving this with other pins on PE as well as other ports on the board. We’ve also tried using a pull-up resistor, but it certainly seems like something else is driving PE4 low.

We’re configuring port E with:

WrPortI(PEDDR, &PEDDRShadow, 0x0f); // Init Port E bit 0,1,2,3 as output, others as inputs
WrPortI(I0CR, NULL, 0x22); // Enable int0 on PE4 (positive edge triggering type / priority)

Any ideas about what we might be overlooking? We’ve studied the schematics that come with the JackRabbit, and there shouldn’t be anything on the BL1810 connected to PE4. Could it be something internal within the processor? We’ve looked at the PE function register, PEFR, but it seems that it should default to normal I/O (and since it’s setup for input, would there be any other configuration needed?).

Any pointers would be appreciated!

Thank you,
Tony Mancill
Washington State University - Vancouver

After removing the JackRabbit board and verifying that the ISR works as expected, I discovered that there is a trace on BL1810 that has to be cut, otherwise PE4 is jumpered to PD0.

Sorry for the noise. Perhaps the post will save someone else the trouble.