It certainly sounds like it to me.

For those who don't know:

When the PIC sets an output bit, it actually does a Read/Modify/Write=20
(RMW) of the whole port.  The Read is of the actual voltage present on=20
the pin, NOT what the output is set to.  So if RB0 is forced high at the=20
time RB1 is set, RB0 will be set to high, even if previous code set it=20
low.  So, if RB0 is driving enough capacitance, the sequence Set RB0,=20
Set RB1 could end with RB0 never going high, whereas Set RA1, Set RB1=20
would work fine.

Kerry


Ruben J=F6nsson wrote:
>> I suspect an electrical difference between ports that I'm missing in the=
=20
>> datasheet as I have discovered by accident that a 1K resistor between=20
>> RB0 and the servo works, I'd still like to know what the difference is=20
>> so I know what/how for future reference and don't get caught again.
>>
>>    =20
>
> If it does work with the resistor and the servo input is a capacitive loa=
d or=20
> draws relatively much current it sounds like an RMW problem. Are any othe=
r bits=20
> in port B written or updated shortly after the servo output is?
>
> The resistor isolates the load from the pic pin and lets it swing to full=
 on or=20
> off much faster than without the resistor.
>
> /Ruben
>
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D
> Ruben J=F6nsson
> AB Liros Electronic
> Box 9124, 200 39 Malm=F6, Sweden
> TEL INT +46 40142078
> FAX INT +46 40947388
> ruben@pp.sbbs.se
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D
>
>  =20



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