Multiplexer address control..

[Dave]

I didn't know we were going for speed....

[richard]

or even this way, constant speed

control        EQU  0x30
latb_shadow    EQU  0x31
LATCH          EQU  0x32   ; simulate lat reg
 

 ORG     ResetVector
 goto    Start


Start
  MOVLW 0
  MOVWF control
  MOVLW 3
  MOVWF LATCH ; eg. LATB,A
lopo
  BANKSEL latb_shadow
  INCF control,F
  MOVLW 0xf
  ANDWF control,F
  
  MOVFF LATCH ,latb_shadow 
  MOVLW 0xf
  andwf latb_shadow ,F  
  SWAPF latb_shadow,F 
  MOVF  control,W
  IORWF latb_shadow ,F
  SWAPF latb_shadow,W
  MOVWF LATCH 
 
  GOTO lopo

  END

[richard]

A little more thought reduces it further,no need at all for a shadow working reg at all
works perfectly on the simulator steps through all 16 "control" states on latb 4-7 and preserves latb 0-3.

; TODO INSERT CONFIG CODE HERE USING CONFIG BITS GENERATOR
  Processor      18f4550
 
  
  include         "p18f4550.inc"   
TRUE  equ 1
FALSE  equ 0
 cblock 0x30 
control     
;latb_shadow   
 endc    
 
 
RES_VECT  CODE    0x0000            ; processor reset vector
    GOTO    START                   ; go to beginning of program
; TODO ADD INTERRUPTS HERE IF USED
MAIN_PROG CODE                      ; let linker place main program
START
   

 



  MOVLW 0f
  MOVWF control
  MOVLW 3
  MOVWF  LATB,A
lopo
  BANKSEL control
  INCF control,F
  MOVLW 0xf
  ANDWF control,F
  
  
  MOVF LATB,A,W
  ANDLW 0XF
  SWAPF WREG,F
  IORWF control,W
  SWAPF WREG,F
  MOVWF LATB ,A
 
  GOTO lopo

[Mike, K8LH]

if I may...

RES_VECT  CODE    0x0000            ; processor reset vector
    GOTO    START                   ; go to beginning of program
; TODO ADD INTERRUPTS HERE IF USED
MAIN_PROG CODE                      ; let linker place main program
START
 

        MOVLW   0f
        MOVWF   control
        MOVLW   3
        MOVWF   LATB,A
lopo
        BANKSEL control
        incf    control,F       ; control = control + 1
        bcf     control,4       ; control = control mod 15
  
        swapf   control,W       ; B7..B4 <- control
        xorwf   LATB,W          ; wreg = differences
        andlw   0xF0            ; ignore B3..B0 bits
        xorwf   LATB,F          ; update B7..B4 bits
 
        GOTO    lopo

[Mike, K8LH]

t'would be simpler/faster still if you were to use the B3..B0 pins as both the 'control' variable and 'control' I/O;

RES_VECT  CODE    0x0000            ; processor reset vector
    GOTO    START                   ; go to beginning of program
; TODO ADD INTERRUPTS HERE IF USED
MAIN_PROG CODE                      ; let linker place main program
START
 

        movlw   0x30            ; B7..B4 other I/O, B3..B0 = control
        movwf   LATB            ;
lopo
        incf    LATB,W          ; B3..B0 bits = control, 0..15
        xorwf   LATB,W          ; wreg = differences
        andlw   0x0F            ; ignore B7..B4 bits (and control mod 16 for free)
        xorwf   LATB,F          ; update B3..B0 bits, 0..15
 
        GOTO    lopo

[richard]

if I may...

Mike, K8LH

that's exactly what a good forum needs

your solution is excellent

[Mike, K8LH]

I like pedja089's solution which is probably about as simple, efficient, and elegant as you can get with pure PBP code. He might test clearing the four LATB bits and then setting them based on if control.0 = 1 then latb.4 = 1 (or something similar).

I have to say the code PBP generated for the "Control << 4" instruction was pretty dismal. I'm curious to see what XC8 will generate for that...