I am using a 16F716 with all portb pins tied to ground through 20k
resistors.  I have also tied portb(4..7) to Vcc through switches and 1k
resistors.  I use portb(4..7) to address a mux and portb(0..3) to drive
relays through a buffer.

I want to be able to read the switches on-the-fly without affecting
portb(0..3).  However, I always get all 1's for the switch setting if I try
to reconfigure portb on-the-fly.  If I only read the switches at the
beginning of the program, I get the correct values.

Here is what I have tried so far (sorry for the parallax):

First I configure portb for outputs so I can run some code:

setb   rp0
mov    trisb,#00000000b
clrb    rp0

Some code goes here...

Then I call this code to read the switches on portb(4..7):

setb    rp0
mov    trisb,#11110000b
clrb    rp0

mov    Temp_lvl,portb
swap   Temp_lvl
and    Temp_lvl,#00001111b

setb    rp0
mov    trisb,#00000000b
clrb    rp0

After this I jump back into my main loop.

I have found that even if I do not write anything to portb after initially
configuring it for all outputs, or even if I write all 0's to portb before
calling my switch reading subroutine, I get all 1's for my switch setting.
The only way the code for reading the switches works is if I only run it
once at the very beginning of the code.

I am wondering how to do this and whether it is possible without affecting
the outputs driving the relays on portb(0..3).

Thanks.

Bruce

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