Post by thread:Help with Ports

Hello, I am confused. If I want to set PortB to output then I do the following from my understanding: movlw 0x00 tris PortB Now PortB is set to output. Now if I do the following: clrf PortB the ports are set to output low. When you set a port to output mode, does the port automatically output high and I have to tell it I want it to go low? Please give code examples and explain. I am missing something!! TIA, Brian ******************************************** Better Produce through Better Control ********************************************

Brian Wrote > I am confused. If I want to set PortB to output then I do the following > from my understanding: > > movlw 0x00 > tris PortB > > Now PortB is set to output. Now if I do the following: > > clrf PortB > > the ports are set to output low. When you set a port to output mode, does > the port automatically output high and I have to tell it I want it to go > low? Please give code examples and explain. I am missing something!! > Nop Its more that you should never trust a PIC (or any micro) to be all nice and cleanly reset after power up. A good old clearing of registers guarantees there are not any stray '1's lurking there. _____________________________ Lance Allen Technical Officer Uni of Auckland Psych Dept New Zealand http://www.psych.auckland.ac.nz _____________________________

<x-flowed>Brian wrote: >Hello, > >I am confused. If I want to set PortB to output then I do the following >from my understanding: > >movlw 0x00 >tris PortB Yes >Now PortB is set to output. Now if I do the following: > >clrf PortB > >the ports are set to output low. When you set a port to output mode, does >the port automatically output high and I have to tell it I want it to go >low? Please give code examples and explain. I am missing something!! When you set a port to output, the bits are as set in it's data register. At the start of your program, you should set the data registers to what you want the initial states to be and also set up the direction registers. (tris) When the PIC resets, the tris registers will be all inputs (11111111) and the data registers are undefined. Best to set data 1st then do your tris 2nd. You can set a bit by doing; bsf PortB,x (where x is the bit you want) The bcf instruction does the same but clears the specified bit. Regards... </x-flowed>