Problems with RC2 and RC3

[mister_e]

O.k, there's few thing to be removed first..

mainloop:
    IF RCSTA.1 = 1 THEN 'if USART overrun error flag OERR is set...
       RCSTA.4 = 0 'clear and then set CREN bit to recover
       RCSTA.4 = 1
       in1 = RCREG 'read data to clear out RCREG
       IF PIR1.5 = 1 THEN in1 = RCREG 'clear possible 2nd byte in RCREG
       ENDIF

DEFINE HSER_CLROERR 1 do this for you. Remove those line.

    WHILE PIR1.5 = 0 'stay here until USART receives data
          'LOW portc.3 'portc.3 has diagnostic LED
          WEND

    'HIGH portc.3 'data in RCREG; turn on diagnostic LED

While your program do nothing usefull there, simply remove those line and replace it simply for HSERIN.

if b1=0 and b2=1 and b3=11 THEN GOSUB ONN1
.
.
.

Should be writen like..

if (b1=0) and (b2=1) and (b3=11) THEN GOSUB ONN1

ONN1:
HIGH PORTB.7
goto mainloop

You jump to ONN1 with a gosub, it must be terminated with a RETURN to avoid stack overflow. Replace GOTO MAINLOOP by a simple RETURN.

Multiple PORTA.0=0, PORTA.1=0, ... can be replace with a single line. In your example you set all PORTA bit to zero. It's working sure, but you can still use PORTA=0. Same for all PORTx to 1. Can be replace with PORTx=%11111111, PORTx=$FF or PORTx=255.

Personnaly i would change it to something different..., let's try something.

    TRISA  = %00000000
    TRISB  = %00000000
    TRISC  = %10000000
    ADCON1 = 7

    PORTx    var byte
    PORTbit  var byte
    BitState var byte    

    PORTA = 0
    PORTB = 0
    PORTC = 0

mainloop:
    hserin 500,mainloop,[PORTx,DEC1 portbit, DEC1 bitstate]
    select case portx
           case "A"
                PORTA.0(PORTBIT)=BITSTATE
           CASE "B"
                PORTB.0(PORTBIT)=BITSTATE
           CASE "C"
                PORTC.0(PORTBIT)=BITSTATE     
           END SELECT
    GOTO MAINLOOP

With few chunk around it may be something to play with

EDIT: also, there's no PORTD on the F870.. no warning or error using PM? I don't know how it's handle by PM but for sure, this will return you an error message when using MPASM...

@Darrel,
Yet another reason