The following from Microchip seems clear...

>From DS30292B-page 33 (the '873 datasheet section 3.3 PORTC and TRISC
Registers):

When enabling peripheral functions, care should be
taken in defining TRIS bits for each PORTC pin. Some
peripherals override the TRIS bit to make a pin an output,
while other peripherals override the TRIS bit to
make a pin an input. Since the TRIS bit override is in
effect while the peripheral is enabled, read-modify-write
instructions (BSF, BCF, XORWF) with TRISC as
destination should be avoided. The user should refer to
the corresponding peripheral section for the correct
TRIS bit settings.

-----

>From DS30292B-page 95 (the '873 datasheet section 10.0n on USART):

Bit SPEN (RCSTA<7>) and bits TRISC<7:6> have to
be set in order to configure pins RC6/TX/CK and
RC7/RX/DT as the Universal Synchronous Asynchro-nous
Receiver Transmitter.

---------- end of cuts from '873 datasheet ----------

In Microchip lingo "set" means make the bit a 1.

The bottom line, don't do read-modify-write operations on a TRIS register
that is controlling pins with another active peripheral, such as the TRISC
register when using the UART or CCP.

---
James Newton (PICList Admin #3)
mailto:jamesnewton@piclist.com 1-619-652-0593
PIC/PICList FAQ: http://www.piclist.com or .org

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Tom Handley
Sent: Saturday, May 13, 2000 00:28
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: 16F873 Uart transmission problem


   Walt, I just took a look at the Mid-Range Reference Manual
(DS31018A) to see if there was any additional info. On page
18-2 they also mention setting the related TRIS Bits though
they are a bit obscure compared to the data books I've used.
Since this comes up fairly often, it would be nice to hear
what Microchip has to say on this.

   - Tom

At 08:31 AM 5/12/00 -0700, Walter Quitt wrote:
>I've dug out my Midrange Referenace manual so
>I can figure our what 2Tad (ADC stuff) is and
>will look at the serial comms references.  I am almost
>sure the ANs associated with serial comms also
>set RC7/RC6 to Input/Output.  But I'm gonna look.
>This is beginning to bug (pun intended) me.  :-)
>-W
>
>-----Original Message-----
>From: Tom Handley [mailto:thandley@TELEPORT.COM]
>
>   Walter, apparently most folks don't have problems setting RC6
>to output but a few have. In anycase, All the data books for All
>the midrange PICs with on-board USARTs say to set Both RC6 and RC7
>to inputs so why not do it? I've been doing that with a variety of
>devices for 5+ years with no problems...
>
>   - Tom

------------------------------------------------------------------------
Tom Handley
New Age Communications
Since '75 before "New Age" and no one around here is waiting for UFOs ;-)