PIC Microcontroller TRIS Instruction

You set the TRIS bits for 0's for the port pins you want to write to; i.e. setting TrisB to '11110000'B would leave RB7..RB4 as inputs but make RB3..RB0 outputs. The TRIS bits are 'usually' write-only; you usually know how you last left them set.

Microchip does not intend to support the TRIS instruction in future products.

In place of a TRIS command, use a MOVWF TRIS(A,B,etc) assuming that W is loaded with the desired mask. You also need to switch to bank 1 before doing the movwf command, where the tris addresses then match the port addresses. That's why people still like to use the tris command - no bank switch is required. If the tris command exists for a chip, it will always exist for that chip - Microchip cautions against using it in the case of using the same software on a future product that will not have the tris command. In the my16F87x data sheet, they emphatically say DONOT USE the tris instruction. In fact, on the '877, the TRIS command works only on ports a, b, c not d, e

Unused pins@, Input/Output@

Questions:

• -Remove-gfbarnet-Remove- at southernco.com asks: " How do I switch to BANK 1 before doing the movwf command?" James Newton replies: Set the appropriate FSR bit in the STATUS register. see http://www.piclist.com/techref/microchip/fr.htm+

  +

Comments:

PICList 2008 contributors: o List host: MIT, Site host massmind.org, Top posters @20081008 Apptech, Jinx, Xiaofan Chen, olin piclist, Vitaliy, Alan B. Pearce, William \Chops\ Westfield, JonnyMac, Tamas Rudnai, Gerhard Fiedler, * Page Editors: James Newton, David Cary, and YOU! * Roman Black of Black Robotics donates from sales of Linistep stepper controller kits. * Ashley Roll of Digital Nemesis donates from sales of RCL-1 RS232 to TTL converters. * Monthly Subscribers: Shultz Electronics, Timothy Weber, on-going support is MOST appreciated! * Contributors: Richard Seriani, Sr.

  .