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I'm using a 12F683 to read a digital sensor, the Sensirion SHT-75.  It is=
 a=20
I2C style interface, but isn't compatible so I'm just doing a software po=
rt=20
instead.  The data line has a external 10K pull up resistor as specified =
by=20
the sensor's data sheet.

The problem I'm having is when I change the GP1 pin to an input.  The sen=
sor=20
should take over the data line and send it's bits serially with the clock=
 I=20
source via the GP0 output.  However the PIC does not seem to read in=20
anything but zeros, even with the line held high.

Here is the code for the read:

	movlw	0x1
	movwf	GPIO		;clock high
	nop                          ;allow settling time
	movf	GPIO,W		;read input
	andlw	0x2		;preserve data bit
	movwf	GPIO		;clock low, use Z bit for result
        return

The port is set as an input before this and I tested it by driving the GP=
1=20
pin low after changing it to an input.  The scope shows the line is high =
so=20
I'm certain the TRISIO register is working right.

This works fine in the simulator (MpLab 7.something) but it is driving me=
=20
nuts trying to sort it out and of course the end product is holding up la=
b=20
work.  Can anyone shine some light on this?  These things usually turn ou=
t=20
to be something obvious I missed but I can't see anything.

Thanks,
Andy

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