decoding quadrature encoders

[HenrikOlsson]

So you're getting ~360 counts for 180 degrees movement. Then the interrupt code must be doing 2x decoding instead of 4x - provided the encoder is actually 360cpr.
You loose the negative value because PBP doesn't handle the multiplication properly and you're of course better off copying the enc_counter variable to a second one for scaling and display purposes, sorry about all that.

Try this (untested):

Degrees VAR WORD
Sign VAR BIT

Degrees = enc_counter   ' Degrees is now -180 to 180
Sign = Degrees.15   ' Save sign
Degrees = (ABS Degrees) * 5   ' Degrees is now 0 to 900
If Sign THEN Degrees = -Degrees   ' Restore sign, value is now -900 to 900

/Henrik.

[cbrun17]

Hi Henrik,

No worries... I learn from mistakes as well. I appreciate all your help.

I believe we're getting very close. I have the following code:


if enc_counter <> enc_counter_old then 'see if value has changed
enc_counter_old = enc_counter 'move new value to old
Counter = enc_counter
Sign = Counter.15 ' Save sign
Counter = ((ABS Counter) * 5) ' Degrees is now 0 to 900

If Sign THEN Counter = -Counter ' Restore sign, value is now -900 to 900

lcdout $FE,1, sdec Counter / 10, ".", sdec Counter //10
lcdout $FE,$C0, sdec Counter


First, the counter increments by 5.
Also, in the first LCD statement, the count increments to +90 as expected. However, the negative value shows as 6553.1, 6552.6, etc...
The second LCD out statement displays +/- 900 as you explained.

Seems the absolute value gets lost when trying to display negative after formatting.

Is there maybe a way I can parse the decimal values prior to display statement to maintain the value?

Chris

[cbrun17]

I made some changes to the formatting and I successfully display the +/- values. Displays +/- xx.x. I updated the code to:

if enc_counter <> enc_counter_old then 'see if value has changed
enc_counter_old = enc_counter 'move new value to old
Counter = enc_counter
Sign = Counter.15 ' Save sign
Counter = ((ABS Counter) * 5) ' Degrees is now 0 to 900
If Sign THEN Counter = -Counter ' Restore sign, value is now -900 to 900

If NOT sign then
lcdout $FE,1, sdec Counter /10 , ".", sdec Counter // 10
else
lcdout $FE,1, "-", sdec -Counter /10 , ".", sdec -Counter // 10
endif

This takes care of displaying properly. Now is there a way I can bring the count down to .25 increments instead of .5?

Thanks again.

Chris

[HenrikOlsson]

Hi,
Great job! The problem with the display routine is, again, that PBP doesn't handle math with negative numbers properly so the result of the Counter / 10 operation gets messed up when Counter is negative.

You can probably make that snippet a bit more efficient, somelike like this perhaps:

if enc_counter <> enc_counter_old then 'see if value has changed
enc_counter_old = enc_counter 'move new value to old
Counter = enc_counter 

Sign = Counter.15 ' Save sign
Counter = ((ABS Counter) * 5) ' Degrees is now 0 to 900

LCDOUT $FE, 1  ' Clear screen
IF Sign THEN
  LCDOUT "-"    ' Print a minus sign if the value is negative
ENDIF
LCDOUT SDEC Counter / 10, ".", SDEC Counter // 10   ' now print the value

I must admit that I can't really follow the ASM code for the interrupt but since it's using Interrupt on change I think it "should" do x4 decoding so you "should" get 1440 counts per revoultion on a 360CPR encoder. I don't know why that's not happening. Hopefully someone else is able to help with that part.

/Henrik.

[cbrun17]

Thank you Henrik.

I couldn't have made it this far without you're help. The displayed number is perfect. As you said, the counts aren't making much sense. I'll continue to experiment with this to see if I can figure out how to get the correct resolution.

Thanks again and kind regards....

Chris

[richard]

you have some isr issues
1.
; Not Necessary for Chips with >2k of Codespace
; movwf wsave
; swapf STATUS, W
; clrf STATUS
; movwf ssave
; movf PCLATH, W
; movwf psave
; Not Necessary for Chips with >2k of Codespace what ?
yet at the end of your isr pclath and status are restored
all isrs need to save and restore mcu status

2.
the chip you are using has more than 1 code pages ,your isr is located in page 0 ,
pclath should be set accordingly
USUAL
ISR BEGIN
movwf wsave
swapf STATUS, W
clrf STATUS
movwf ssave
movf PCLATH, W
movwf psave
CLRF PCLATH
YOUR CODE
.............
3.
a RE stream moving clockwise goes phase 1 - 2 - 3 - 4 -1 -2 .......
where phase 1=00
2=10
3=11
4=01
your code
;check to see if encoder has moved
movf _enc_old,W ;move enc_old to W
movwf _enc_tmp ;put W to enc_tmp
movf _enc_new,W ;move enc_new to W for XOR
xorwf _enc_tmp,F ;XOR enc_tmp to detect encoder movement
btfsc _enc_tmp,7 ;if bit is clear, encoder moved.
goto Continue ;no movement exit isr


say enc_old=01 ,enc_new=00 ; ie clockwise move
your xor would yield 0b01000000
and bit 7 is clear so no move is recorded , wrong it did move .it may also cause the 0 point to creep as direction
changes occur
the test should be is the result 0 not is bit7 0

4. bank sel ?
your isr forces bank0 the chip has more than one bank available
all vars used in isr need to be assigned to bank 0
ie enc_old VAR BYTE bank0 .
etc
5. enc_counter a word a non atomic entity
any non atomic entity that can be changed in an isr and is used outside the isr needs to be handled
correctly to prevent glitches caused by rollover/under of the low byte.
best way is to use a buffered copy or that entity
eg

enc_counter VAR WORD bank0
buffered_enc_counter VAR WORD
gosub get_enc_count


get_enc_count:
intcon.3=0 ; rbc_int off
buffered_enc_counter=enc_counter
intcon.3=1 ; rbc_int on
return

[cbrun17]

Hi Richard,

Thank you very much for the information. It's a little over my head at this point with regard to asm. I'm still very new to asm coding, but I'm going to try working through your suggestions and see what I can accomplish.

Chris

[cbrun17]

Hi Richard,

Here is what I've done so far. Since I'm just learning asm (and coding in general), I made the changes you suggested as I understand them (haven't tried to compile yet). The part I am still not too sure about is the reference to is testing bit7. Are you saying I should not be testing bit7 (btfsc _enc_old,7)? How do I reference this in the asm code?

I've tried going through this step by step and it's starting to make a little sense. I guess until I've done this a few times, I'll have to ask some lame questions....

Again, I really appreciate your input.

'Read Quadrature Encoder and display value on LCD. for ****pic16f876****

'************************ DEFINES HERE *************************************
DEFINE OSC 20               ' set to 20mhz
DEFINE LCD_DREG PORTA       ' Set Data Registers port
DEFINE LCD_DBIT 0           ' Set starting data bit
DEFINE LCD_RSREG PORTB      ' Set LCD RS Port
DEFINE LCD_RSBIT 1          ' Set LCD RS Bit
DEFINE LCD_EREG PORTB       ' Set LCD Enable Port
DEFINE LCD_EBIT 2           ' Set LCD Enable Bit
DEFINE LCD_BITS 4           ' Set LCD 4bit Mode
DEFINE LCD_LINES 2          ' Set number of LCD Lines
DEFINE LCD_COMMANDUS 2000   ' Set Command Delay time in uS
DEFINE LCD_DATAUS 60        ' Set Data delay time in uS 

clear                       'clear out variables

'*********************** CHIP REGISTER SETUP *******************************

ADCON0 = 7              ' turn off analog porta, set to digital IO
ADCON1 = 7              '
CMCON =  7              ' Turn off Port A Comparator
TRISA = 0               ' output ports
TRISB = %11000001       ' set input and output ports
TRISC = 0               ' output ports

'************************ PROGRAM VARIABLES HERE ***************************

symbol led = portc.2         ' status led
symbol led2 = portc.0       ' status led2
symbol lcdbkl = portc.7     ' lcd pannel backlight
symbol sw1 = portb.0       ' encoder switch

enc_old 	          VAR     BYTE
enc_new 	          VAR     BYTE
enc_tmp 	          VAR     BYTE
enc_counter 	  	  VAR    WORD bank0
enc_counter_old  	  VAR    WORD bank0
enc_scaler 	  	  VAR    WORD bank0


'*********************** ASSEMBLY INTERUPT VARIABLES ***********************
wsave     VAR     byte $20 system
wsave1    VAR     byte $a0 system  ' Necessary for devices with RAM in bank1
wsave2    VAR     byte $120 system ' Necessary for devices with RAM in bank2
wsave3    VAR     byte $1a0 system ' Necessary for devices with RAM in bank3
ssave     VAR     byte bank0 system
psave     VAR     byte bank0 system     

    goto start			'skip over interupt handler

'*********************** ASSEMBLY INTERUPT HANDLER *************************

define  INTHAND myint
Asm
       
myint 
	; Save W, STATUS and PCLATH registers
	; Not Necessary for Chips with >2k of Codespace
	
	; ****Changed from original isr initialization settings****
        ;movwf   wsave
        ;swapf   STATUS, W
        ;clrf    STATUS
        ;movwf   ssave
        ;movf    PCLATH, W
        ;movwf   psave  
         
; Changed from original isr initialization settings
	movwf wsave
 	swapf STATUS, W
 	clrf STATUS
 	movwf ssave
 	movf PCLATH, W
 	movwf psave 
 	CLRF PCLATH


	;====== BEGINNING OF THE ROTARY ENCODER CODE ========
	;The Rotary Encoder is connected to PORTB  
	;The A signal of the encoder connected to the PIN portB.7
	;The B signal of the encoder connected to the PIN portB.6
	;
	;The 4 variables used are declared in the PicBasic code.
	;
	;	enc_new VAR BYTE
	;	enc_old VAR BYTE
	;       enc_tmp VAR BYTE
	;	enc_counter VAR WORD
	;
	;================================================
		
	   ;Read latest input from PORTB & put the value in _enc_new.
     	movf    PORTB,W
     	movwf  _enc_new

     	;Strip off all but the 2 MSBs in _enc_new.
     	movlw	0xc0    	     ;Create bit mask (bits 7 & 6). b'11000000' ?
     	andwf   _enc_new,F       ;Zero bits 5 thru 0.

        ;check to see if encoder has moved
        movf    _enc_old,W         ;move enc_old to W
        movwf   _enc_tmp           ;put W to enc_tmp
        movf    _enc_new,W         ;move enc_new to W for XOR
        xorwf   _enc_tmp,F         ;XOR enc_tmp to detect encoder movement
        btfsc   _enc_tmp,7         ;if bit is clear, encoder moved.       ************Not sure what needs to happen here**************
        goto    Continue           ;no movement exit isr

     	;Determine the direction of the Rotary encoder.  
     	rlf     _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 ************Not sure what needs to happen here**************
      	                         ;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.
     	bsf     _led		    ;turn on led
     	
     	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.
	   bsf     _led2		    ;turn on led
	
Continue     	
     	;Assign the latest encoder inputs (in _enc_new) to _enc_old.
     	movf 	_enc_new,W
     	movwf   _enc_old

        ; Restore saved registers
        movf    psave, W
        movwf   PCLATH
        swapf   ssave, W
        movwf   STATUS
        swapf   wsave, F
        swapf   wsave, W
        bcf     INTCON, RBIF		  ; Clear the Interupt Flag
        RETFIE                 	  	  ; Return from interrupt
endasm

'***************************************************************************
'************************* PROGRAM STARTS HERE *****************************
'***************************************************************************

START:              ' Main Program starts here

   LCDOUT $FE,1		'Init The LCD
      pause 500		    'wait for LCD to start 

   LCDOUT $FE,1,"ENCODER"	    'display splash screen
   LCDOUT $FE,$C0," TEST "       
     high lcdbkl                 ' turn on backlight


'************************** SET DEFAULT SETTINGS HERE **********************
pause 1000		    ' just wait a bit to read splash screen
enc_counter = 0	' set default encoder value
enc_counter_old = 0	

        ' Initial display
    LCDOUT $FE,1,"ENCODER"  ' Initial display
    LCDOUT $FE,$C0, "00.00"

INTCON = %10001000      ' Enable PortB Change Interupts  


'************************** TESTING ROUTINES HERE **************************

test:
	  
            if buffered_enc_counter <> enc_counter_old then 'see if value has changed
               	'enc_counter_old = enc_counter 'move new value to old ******Removed this line and replaced with*******
                 
                gosub get_enc_count                                  '******this line******************************

 		 Counter = buffered_enc_counter
 
 		Sign = Counter.15 ' Save sign
 		Counter = ((ABS Counter) * 5) ' Degrees is now 0 to 900
 	If Sign THEN Counter = -Counter ' Restore sign, value is now -900 to 900

 	   If NOT sign then
 		LCDOUT $FE,1, sdec Counter /10 , ".", sdec Counter // 10 
 	   else
 		LCDOUT $FE,1, "-", sdec -Counter /10 , ".", sdec -Counter // 10
 	   endif

'*********************************************************************************

                low led		                        'turn off CCW led
                low led2	                        'turn off CW led
            endif
goto test

get_enc_count:
 intcon.3=0 ; rbc_int off
 buffered_enc_counter=enc_counter
 intcon.3=1 ; rbc_int on
 return