PIC Controller Help

[JoshMac]

Hi Peoples,

Can anybody show me whats wrong with this code?!? The code appears to run fine, however, it will not allow me to change the TRISA or TRISB (TRIS A & B are stuck on 11111111). Programming in MPLAB 8.92. The code responds to virtual stimulus on the pins. Is there a register I am missing?

Thanks,
Josh

Code: Select all

   list     p=16F628A            ;SET CHIP MODEL
   #include <p16F628A.inc>         ;INCLUDE DEFAULTS
   __CONFIG _CP_OFF & _WDTE_OFF & _BODEN_ON & _PWRTE_OFF & _LVP_OFF & _CPD_OFF & _INTOSC_OSC_NOCLKOUT & _MCLRE_OFF   ;LOAD CONFIG SETTINGS
   ORG 0x0000                  ;SET ORIGIN TO 0X000

   MOVLW      0X07               ;ALL COMPARATORS TO OFF
   MOVWF      CMCON            
   BSF         STATUS,RP1         ;SELECT BANK0
   MOVLW      0X00               ;SET PORT A DIRECTION
   MOVWF      TRISA
   MOVLW      0x00               ;SET PORT B DIRECTOIN
   MOVWF      TRISB
   CLRF         INTCON            ;SWITCH OFF ALL INTERUPTS
   BCF         STATUS,RP1         ;SELECT BANK0

START
   MOVLW      0xFF
   MOVWF      PORTB
   MOVWF      PORTA

END


[pebe]

It's because that's all you have asked the program to do.

After initializing the ports, your program begins at 'Start' with the instruction to load reg 'w' with FF. Then copy 'w' to both ports. There the program ends and you are left with FF at both ports.

How do you want to change them? As both ports are set as outputs you have no means to input a change.

[JoshMac]

Hi Pepe,

The problem was that although I was asking it to change the TRIS A & B register, the change was not actually happening both in simulation and on board. After lots of playing around i found that it wasn't switching over to bank 1, so the process was effectively trying to change a reg called TRISA and TRISB in bank0 (which does not exist). Im not sure why, but i think it might have something todo with the include file, perhaps not understanding what "RP1" is. I changed it to modify the bit instead and everything appears to work.

As always - thanks for the help,
Josh

[pebe]

Hi Josh,
I'm glad you managed to sort it out. The problem was you were toggling RP1 to change banks, whereas you should have been toggling RP0.

If you look at page 17 of the data sheet for that PIC, you will see in Table 4-2 that RP0 and RP1 are bits of the Status register, which can be accessed from any bank. There are four banks (0 to 3) and RP1 selects either the top or bottom two, and RP0 determines whether banks 0/2 or 1/3 are selected.

Table 4-3 on page 20 shows the bits of the Status register. RP0 and RP1 are bits 5 and 6, so you could also change between bank 0 and 1 with 'SET STATUS,5' or 'RES STATUS,5'.

I hope that has helped.