Can PBP read optical encoder damn fast? :)

[louislouis]

For optical encoder I use this:

; PIC18F4520 

DEFINE OSC 4

INCLUDE "DT_INTS-14.bas"        ; Base Interrupt System
INCLUDE "ReEnterPBP.bas"        ; Include if using PBP interrupts

TRISA    = %00000000 ' Make all PortA pins output
TRISB    = %11001000

Define LCD_DREG PORTA
Define LCD_DBIT 0
Define LCD_RSREG PORTA
define LCD_RSBIT 4
define LCD_EREG PORTA 
define LCD_EBIT 6
define LCD_BITS 4
define LCD_LINES 2
define LCD_COMMANDUS 2000
define LCD_DATAUS 50

; encoder ch A PortB.6
; encoder ch B PortB.7

wsave       VAR BYTE $70     SYSTEM  ; alternate save location for W 
enc_new     VAR BYTE bank0
enc_old     VAR BYTE bank0
enc_counter VAR word bank0
Flag        var BYTE bank0

asm
INT_LIST  macro    ; IntSource,        Label,  Type, Resetflag?
        INT_Handler    RBC_INT, _enc,  ASM,  yes
    endm
    INT_CREATE     ; Creates the interrupt processor
endasm

; Set variable value @ startup       
enc_new = 0
enc_old= 0
enc_counter = 0
Flag = 0
@ INT_ENABLE RBC_INT  ; enable external (INT) interrupts 

Main_Loop:                                         
Lcdout $fe, 1
lcdout  Dec enc_counter  
goto Main_Loop

enc:
asm    
    ;Read latest input from PORTB & put the value in _enc_new.
         MOVE?CB 1,_Flag
         movf    PORTB,W
         movwf  _enc_new
                               ;Strip off all but the 2 MSBs in _enc_new.
         movlw    B'11000000'  ;Create bit mask (bits 7 & 6).
         andwf   _enc_new,F    ;Zero bits 5 thru 0.
                               ;Determine the direction of the Rotary encoder.  
         rlcf     _enc_old,F   ;left shift it into _enc_old to align bit 6 of 
                               ;_enc_old with bit 7 of _enc_new.
         movf    _enc_new,W    ;Move the contents of _enc_new to W in order to XOR.
         xorwf   _enc_old,F    ;XOR previous inputs (in _enc_old) with latest
                               ;inputs (in W) to determine CW or CCW.
 
         btfsc   _enc_old,7    ;Test bit 7 of result (in _enc_old).  Skip next line
                               ;if it is 0 (direction is CCW).
         goto    Up            ;Bit is 1 (direction is CW).  Go around Down
                               ;and increment counter.

Down
     ;Decrements _enc_counter because the rotary encoder moved CCW.
     ;Decrements _enc_counter (16 bit value), sets Z on exit.
              
        decf    _enc_counter,F      ; Decrement low byte
        incfsz  _enc_counter,W      ; Check for underflow
        incf    _enc_counter+1,F    ; Update
        decf    _enc_counter+1,F    ; Fixup
        movf    _enc_counter,W
        iorwf   _enc_counter+1,W    ; Set Z bit
        
    ;Add here code for the CCW LED if needed.
         
         goto    Continue          ;Branch around UP.
Up
    ;Increments _enc_counter because the rotary encoder moved CW.
    ;Increments _enc_counter (16 bit value), sets Z on exit.
        incfsz  _enc_counter,W      ; Add one to low byte
        decf    _enc_counter+1,F    ; No carry (negates next step)
        incf    _enc_counter+1,F    ; Add one to high byte
        movwf   _enc_counter        ; Store updated low byte back.
        iorwf   _enc_counter+1,W    ; Set Z flag
        
    ;Add here code for the CW LED if needed.
    
Continue 
         
    ;Assign the latest encoder inputs (in _enc_new) to _enc_old.
         movf     _enc_new,W
         movwf   _enc_old
         INT_RETURN
    ;============ END OF THE ROTARY ENCODER CODE =====
    endasm

[CuriousOne]

Yes I checked that PIC datasheet already, but I don't see any ways to implement it in PBP, we don't have statement for encoder reading, like we have for LCDOUT or OWIN.

[CuriousOne]

I've modified my code and it works ok, but sometimes I get false readings too - say for 20 pulses of CW, I will have 2-3 pulses of CCW and vise versa

STATE: 'WAIT FOR ENCODER TO BE MOVED (STATE CHANGE)
'Lcdout $Fe, $1, "WAIT..." , DEC ENX, " ", DEC ENY
X=ENX
Y=ENY
PAUSE 1
X1=ENX
Y1=ENY
IF X<>X1 OR Y<>Y1 THEN GOTO SOMELOOP
GOTO STATE


SOMELOOP: 'COUNTER LOOP FOR PULSE LENGTH COUNTING
IF ENX=1 THEN X1IN=X1IN+1 'X INCREMENT
IF ENY=1 THEN Y1IN=Y1IN+1 'Y INCREMENT
IF ENX=0 and ENY=0 THEN GOTO ANALYZE 'EXIT AND COMPARE LENGTHS
PAUSE 1
GOTO SOMELOOP


ANALYZE: 'DETERMINE DIRECTION AND INCREMENT CORRESPONDING VARIABLE
IF X1IN>Y1IN THEN 
CCW=CCW+1
ELSE
CW=CW+1
ENDIF
LCDOUT $FE, $1, "RAW", DEC Y1IN, "  ", DEC X1IN, "  "
LCDOUT $FE, $C0, "VAL ", DEC CCW, "  ", DEC CW, "  "
PAUSE 1
X1IN=0 'RESET VARIABLES
Y1IN=0 
GOTO STATE

[CuriousOne]

This is simple 3 pin incremental encoder, middle pin is tied to VCC, A and B are tied to PORTB.3 PORTB.4, which are also pull down with 10K resistors. If I rotate shaft slowly, then no false readings. What can be reason, some wiring issue or code inefficiency?

[Ioannis]

This is simple 3 pin incremental encoder, middle pin is tied to VCC, A and B are tied to PORTB.3 PORTB.4, which are also pull down with 10K resistors. If I rotate shaft slowly, then no false readings. What can be reason, some wiring issue or code inefficiency?

Well, your LCD may be slowing down the response. And since you use PAUSE and LCDOUT it is expected that program is not the most efficient. The encoder is best done in ISR and even better using hardware module when available.

Ioannis

[CuriousOne]

I don't see how to avoid use of pause statement. We have time changing, things are happening within time, so how not to consider time? In final device, there will be no LCDOUT, if that is the problem.

[Ioannis]

ISR then.

Ioannis

[Ioannis]

Yes I checked that PIC datasheet already, but I don't see any ways to implement it in PBP, we don't have statement for encoder reading, like we have for LCDOUT or OWIN.

What stops you from writing directly to the registers?

Ioannis