This is a second try to get the 16F685 working to respond on a signal change
on RB7.
I wrote this small piece of code on advise earlier after the first question
about this.
 
When i set a signal on RB7 niether RA0 or RA1 or both wil come on. Thit i
missed something in the datasheet on this matter. As far i can see i have
set all the registers correct.
 
;        errorlevel      -302, -305  ; Suppress Bank Warnings
            list        p=16F685, r=hex
            INCLUDE     "P16F685.INC"
            __CONFIG    0x3CE2
; --- Definetions section
----------------------------------------------------
; --- Macros definitions

; --- Constant values
#define     DCCIN   PORTB, 7        ; DCC signal input
 
; --- Variables in RAM
    cblock  0x070                   ; On bottom of all banks
INT_W                               ; Interrupt context registers
INT_STAT                            ;
EEDATA0                             ; EEPROM shadow variables
    endc
 
; --- Program section
--------------------------------------------------------
    org 0x000
PowerUp:
    clrf    STATUS                  ; Bank0 is default
    clrf    INTCON                  ; Disable all interrupts at first
    clrf    PCLATH                  ; All tables on Bank0
                                    ; Following the datasheet the above
could
                                    ; onmitted but we use it to be sure
    goto    Init
; --- Interrupt routine
------------------------------------------------------
    org 0x004
Interrupt:
    movwf      INT_W                   ; Save content register
1
    swapf       STATUS, W               ;
2
    movwf      INT_STAT                ;
3
    clrf          STATUS                  ; Interrupt uses BANK0
4
 
    btfsc        DCCIN                   ; DCC signal present
5
    
    bsf           PORTA, 0
    bsf           PORTA, 1
    nop
 
EndInt:
    swapf       INT_STAT, W             ; Restore content registers       49
34
    movwf      STATUS                  ;                                 50
35
    swapf      INT_W, f                ;                                 51
36
    swapf      INT_W, w                ;                                 52
37
    retfie                          ;                              53 54 38
39
; --- Set used registers in correct setting
----------------------------------
Init:
                                    ; These registers are in BANK0
    clrf         PORTA
    clrf         PORTB
    clrf         PORTC
 
    BANKSEL TRISA                   ; These registers are in BANK1
    clrf        TRISA                   ; Set to all outputs
    movlw   b'10110000'             ; Set RB7, RB5 and RB4 to Input
    movwf   TRISB
    clrf        TRISC                   ; Set to all outputs
    movlw   b'10001000'              ; Set Optionregister  to no PullUps,
                                              ; no prescaller and WDT 1:1
    movwf   OPTION_REG
    clrf       WPUA                    ; Dont use WeakPullUp on PORTA
                                              ; We dont use IOC on PORTA so
leave it as  it is
 
    BANKSEL ANSEL                   ; These registers are in BANK2
    clrf         ANSEL                   ; Set to all digital I/O
    clrf        ANSELH
    clrf        WPUB                    ; Dont use WeakPullUps on PORTB
    movlw   b'10000000'             ; Set RB7 to InterruptOnChange PORTB
    movwf   WPUB
 
    BANKSEL 0x00                    ; Return to BANK0
    movlw   b'00110001'             ; Set Timer1 on at 1:8
    movwf   T1CON
    movlw   b'10001000'             ; Enable all unmasked interrupts and
                                             ; enable PORTA/PORTB interrupt
on change
    movwf   INTCON
 
    nop
    bsf     PORTC, 2
    nop
    goto    $
    end
 
Regards
 
Harry
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