Many PICs have pins that are input only.  Table 1-3 of the
PIC24FJ128GB204 Family datasheet shows that RA4 and RB4 are input only.
Seems to me that it is usually only one pin, tho, and for some reason
that seems to often be RA5.  Don't know why this one is different.

--McD

On Mon, 2015-10-26 at 08:31 -0400, Anthony Toft wrote:
> Hi,
>=20
> I have recently started a hobby project using the PIC24FJ128GB202 (in a=20
> 28-pin SOIC package) mainly for the built in USB transceiver and am=20
> having a problem with the HD44780U I am using...
>=20
> Bear in mind the board has not been etched yet, and this is purely for=20
> my own education as I have spare pins that I can use as a work around.
>=20
> I have the control lines (E RW and RS) connected to RA4, RB4 and RB5 in=20
> the data sheet these are pins 12, 11 and 14 respectively. However,=20
> trying to set and clear the necessary TRIS and LAT bits for these pins=20
> causes compile errors with XC16. I looked at the relevant header file=20
> and discovered that the bits were missing from the bitfields, so I=20
> understand why the compile is failing, but that brought up the question=20
> why are they missing?
>=20
> Could this be a copy and paste error? Are there reasons not to use these=
=20
> pins?


--=20
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