Status: New
Owner: robhamerling
Labels: Type-Defect Priority-Medium Component-Device
New issue 169 by robhamerling: Flipping a pin with the 18F PICs
http://code.google.com/p/jallib/issues/detail?id=169
Failing 'alternative' blink-a-led program with an 18F (18F67k90).
This works:
forever loop
led = true -- on
_usec_delay(250_000)
led = false -- off
_usec_delay(250_000)
end loop
This doesn't work (the LED doesn't blink):
forever loop
led = !led -- flip
_usec_delay(250_000)
end loop
I thought that we agreed on the principle: always read from PORTx and
always write to LATx (for PICs which have LATx registers).
Therefore in the Jallib device files of the 18F and extended midrange PICs
a read from a port or pin always uses the PORTx register, while a write to
a port or pin always uses the LATx register (via pseudo variables).
The first case above there are only writes to the pin involved (to LATx
register), so there is no read involved.
In the second case however the pin has to be read before it can be flipped
properly. Thus the current state of the led-pin is read from the PORT
register and the flipped state written to the LAT register. But this seems
not to work (in this case).
When writing to a pin it has probably(!) been configured (via TRIS) for
output. The question is: must in this case the PORT register be read or the
LAT register?
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