decoding quadrature encoders

[mat janssen]

Here is a small example how to count up and down a position counter.
How to initialise the position counter you must do by yourself.

A_INPUT VAR PORTA.0
B_INPUT VAR PORTA.1

HULP1 VAR BIT
HULP2 VAR BIT

COUNTER VAR WORD

Clear
COUNTER = 32768

START:


HULP2 = A_INPUT & ~ HULP1 'EVERY POSITIVE GOWING EDGE OF A_INPUT
HULP1 = A_INPUT 'GIVES A PULSE OF ONE PROGRAMM CYCLE

IF HULP2 = 1 AND B_INPUT = 1 THEN 'MOTOR TURNS RIGHT
COUNTER = COUNTER + 1
ENDIF

IF HULP2 = 1 AND B_INPUT = 0 THEN 'MOTOR TURNS LEFT
COUNTER = COUNTER - 1
ENDIF

[Luciano]

Hi!

Maybe these two links will help you out.

Nuts and Volts:
http://www.parallax.com/dl/docs/cols...l1/col/nv8.pdf

See State machine: two-bit quadrature encoder
http://www.emesystems.com/BS2fsm.htm#twobit%20encoder

Luciano

[ice]

mat janssen>>
Thank yoiu very much for the code snip..but i cant understand whats going on in the code ,esp the "&~" part
I tried using the code...however ,whatever maybe the direction the motor is running ....i get the same reading ,say always "left"



Luciano>>
Thanks for the links..
i ported the foll code from nv8 [http://www.parallax.com/dl/docs/col...ol1/col/nv8.pdf --pg7]

    let new = pins & %11000000 ' Mask off all but bits 6 & 7
start:
   let old = new & %11000000 ' Mask bits and copy new into old.
again:
   let new = pins & %11000000 ' Copy encoder bits to new.
   if new = old then again ' If no change, try again.
   let directn = bit6 ^ bit15 ' XOR right bit of new w/ left bit of old.
   if directn = 1 then CW ' If result=1, encoder turned clockwise.
   serout 0,n2400,(I,left) ' If result=0, counterclock (scroll left).
   goto start ' Do it again.
CW:
   serout 0,n2400,(I,right) ' Clockwise (scroll right).
   goto start ' Do it again.

To pbp

old VAR BYTE
new VAR BYTE
direct VAR BIT

quad:
	new= PORTC && %00000011
	
start:
	old=new && %00000011

again:
	new= PORTC && %00000011
	Pause 10
	LCDOut $fe,1,"no movement"	
	IF new=old Then again
	direct=new.bit1 ^ old.bit0	
	IF direct=0 Then GoTo cw
	LCDOut $fe,1,"one dir"
	Pause 10
	GoTo start
		
cw:
	LCDOut $fe,1,"2nd dir"
	Pause 10
	GoTo start

with the above code...there is alot of fluctuation between the 2 directions..

..anything going wrong in my code?.i sat on it the whole day..still cant figure out the problem

[mat janssen]

Hallo,
I completed the programm for testing and it works ok.
With the & ~ look in the manual it takes the not value of the bit.

here is the complete source and also the hex file

'PIC 16F628A test


@ DEVICE PIC16F628A,INTRC_OSC
@ DEVICE PIC16F628A,MCLR_OFF
@ DEVICE PIC16F628A,BOD_OFF
@ DEVICE PIC16F628A,LVP_OFF
@ DEVICE PIC16F628A,CPD_OFF
@ DEVICE PIC16F628A,PROTECT_OFF


DEFINE OSC 4




CMCON = 7
VRCON = 0
OPTION_REG.7 = 0

TRISA = %11111111
TRISB = %00000000


A_INPUT VAR PORTA.0
B_INPUT VAR PORTA.1

HULP1 VAR BIT
HULP2 VAR BIT

COUNTER VAR WORD

Clear

COUNTER = 128

START:


HULP2 = A_INPUT & ~ HULP1 'EVERY POSITIVE GOWING EDGE OF A_INPUT
HULP1 = A_INPUT 'GIVES A PULSE OF ONE PROGRAMM CYCLE

IF HULP2 = 1 AND B_INPUT = 1 Then 'MOTOR TURNS RIGHT
COUNTER = COUNTER + 1
EndIF

IF HULP2 = 1 AND B_INPUT = 0 Then 'MOTOR TURNS LEFT
COUNTER = COUNTER - 1
EndIF

PORTB = COUNTER
GoTo START

[Luciano]

Hello ICE!

You need the Bitwise Operator:
&

Not the logical Operator AND:
&& (AND and && are the same)


From the PBP manual:

4.17.14. Bitwise Operators

Bitwise operators act on each bit of a value in boolean fashion.
They can be used to isolate bits or add bits into a value.


4.19. Logical Operators

Logical operators differ from bitwise operations. They yield a true/false
result from their operation. Values of 0 are treated as false. Any other
value is treated as true.


Luciano

[ice]

Luciano,
I tried it with & [bitwise operators]...actually everything..
still no go...

mat janssen>>
are u by any chance using a dual D f/f between the encoder and the PIC,because im not..
Thanks for ur code snip

[mat janssen]

No, this small programm reacts as a D flipflop.
see attached drawing what happens

[Luciano]

Hello ICE,

From the PDF file page 3:
http://www.parallax.com/dl/docs/cols...l1/col/nv8.pdf

In the case of the encoder sequence, it turns out that for
any given sequence, XORing the righthand bit of the old value
with the lefthand bit of the new value tells you the direction
of rotation.
For example, take the clockwise sequence 01 00: 1 XOR 0 = 1.
Now the counter-clockwise sequence 01 11: 1 XOR 1 = 0.
This relationship holds for any pair of numbers in either direction.

* * *
The code for the above is:

direction_bit = old.bit0 ^ new.bit1 ' 1 if CW, 0 if CCW

* * *
In your code:

Pause 10 '= 10 milliseconds

* * *
This will help you to debug your code.

Remove the line
LCDOut $fe,1,"no movement"

Replace the lines
LCDOut $fe,1,"one dir" with LCDOut $fe,1,"Last direction was CCW"
LCDOut $fe,1,"2nd dir" with LCDOut $fe,1,"Last direction was CW"


Luciano

[ietcyberwolf]

Hallo,
I completed the programm for testing and it works ok.
With the & ~ look in the manual it takes the not value of the bit.

here is the complete source and also the hex file

'PIC 16F628A test


@ DEVICE PIC16F628A,INTRC_OSC
@ DEVICE PIC16F628A,MCLR_OFF
@ DEVICE PIC16F628A,BOD_OFF
@ DEVICE PIC16F628A,LVP_OFF
@ DEVICE PIC16F628A,CPD_OFF
@ DEVICE PIC16F628A,PROTECT_OFF


DEFINE OSC 4




CMCON = 7
VRCON = 0
OPTION_REG.7 = 0

TRISA = %11111111
TRISB = %00000000


A_INPUT VAR PORTA.0
B_INPUT VAR PORTA.1

HULP1 VAR BIT
HULP2 VAR BIT

COUNTER VAR WORD

Clear

COUNTER = 128

START:


HULP2 = A_INPUT & ~ HULP1 'EVERY POSITIVE GOWING EDGE OF A_INPUT
HULP1 = A_INPUT 'GIVES A PULSE OF ONE PROGRAMM CYCLE

IF HULP2 = 1 AND B_INPUT = 1 Then 'MOTOR TURNS RIGHT
COUNTER = COUNTER + 1
EndIF

IF HULP2 = 1 AND B_INPUT = 0 Then 'MOTOR TURNS LEFT
COUNTER = COUNTER - 1
EndIF

PORTB = COUNTER
GoTo START

I'm trying to do the example with PIC16f877a but i have problems for example the VRCON = 0 my compiler says it's a bad instruction how can i probe with this pic

thanks

[Ioannis]

877A does not have VRCON register. Instead it has CVRCON.

Look in the P16F877A.inc file in the C:\Program Files\Microchip\MPASM Suite path.

Also pf of the chip you are using is a must.

Ioannis

[ietcyberwolf]

Hi Ioannis exactly i'm using PIC16f877a i have the same problem that ice i cant see my count on my LCD and i cant see using pbp
only add my count never sub my count do you know what's my problem?

i tried all in my hands but i continue with same errors
My code is:

'****************************************************************
'*  Name    : UNTITLED.BAS                                      *
'*  Author  : .                                                            *
'*  Notice  : Copyright (c) 2011 [Ing..]  *
'*          : All Rights Reserved                               *
'*  Date    : 19/04/2011                                        *
'*  Version : 1.0                                               *
'*  Notes   :                                                   *
'*          :                                                   *
'****************************************************************
'Parte de configuraciÛn de LCD
DEFINE LCD_DREG PORTB
DEFINE LCD_DBIT  4
DEFINE LCD_RSREG PORTB
DEFINE LCD_RSBIT 1
DEFINE LCD_EREG  PORTB
DEFINE LCD_EBIT  3
DEFINE OSC 4

contador var byte
ON INTERRUPT GOTO SUMA
INTCON.4 = 1
INTCON.7 = 1
OPTION_REG.6 = 1  
CMCON=7
CVRCON=0

TRISB = %00000101
CONTADOR = 12

principal:
lcdout $FE,1,"ENCODER= ",#CONTADOR," VALOR "
pause 500
goto principal
DISABLE
end

SUMA:
IF PORTB.0 = 1 THEN
    OPTION_REG.6 = 0
    IF PORTB.2 = 1 THEN
    contador = contador + 1
    ENDIF
else
    OPTION_REG.6 = 1
    IF PORTB.2 = 1 THEN
    CONTADOR = CONTADOR - 1
    ENDIF
ENDIF
INTCON.1 = 0
RESUME
ENABLE

[ChrisMicro]

Hi mat I see you are using ASM to set up your config word, it is a greate idea, but I get a compiler error when I do it. I always edit the device include file 16F628.INC:
NOLIST
ifdef PM_USED
LIST
include 'M16F62x.INC' ; PM header
device pic16F628, intrc_osc, wdt_off, pwrt_off, mclr_off, lvp_off, protect_off
XALL
NOLIST

[mister_e]

With PBP3 you no longer need to comment out the INC file.

BTW you should'nt edit it each and every time. Comment out the DEVICE and CONFIG lines in the INC file, save it... and set the fuses on your code period.

If you still experiment compiler error or warning, check out the syntax used.. is it PM or MPASM... PM need DEVICE line(s), while MPASM need __CONFIG line(s)

Better get familiar with MPASM syntax though... PBP3 use it, PM is no longer supported.

[cbrun17]

Hello,

I know this is an old thread but I have reached the extent of my knowledge with PBP. I have been testing the code published by several forum members and the code works wonderful. Using the asm interrupts provides very fast response and no missed counts. The issue I have is trying to display the results on LCD in 4 digit result (xx.xx). I'm using the following hardware:

16F876 @ 20MHz
US digital S4T-360 (360 CPR)
2x16 LCD connected to PortA

I'm using the encoder to measure angles from a center position (12 o'clock). It can turn +/- 90 degrees. I need to display the results as +/- any value between 0 and 90 such as 46.15 or -58.23 (cw,ccw respectively).

Since the count value is one byte, I can't figure out a way to get greater resolution for the count. I'm very new to programming period!!! I realize I have a lot to learn and I will continue to learn.
I've tried using sdec enc_Count/10, enc_count//10 in the LCD lines but the results are not giving me what I need.

Maybe I'm missing something really simple and I hope someone can point me in the right direction.

Here is the code I'm using:

'Read Quadrature Encoder and display value on LCD. for pic16f876a

'setup PIC Config Fuses
    @ Device pic16F876A, HS_OSC, BOD_OFF, PWRT_ON, WDT_OFF, PROTECT_OFF

'************************ 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
enc_counter_old VAR WORD
enc_scaler var word




'*********************** 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
       ; movwf   wsave
       ; swapf   STATUS, W
       ; clrf    STATUS
       ; movwf   ssave
       ; movf    PCLATH, W
       ; movwf   psave  
         



	;====== 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.
        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
      	                         ;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	

lcdout $FE,1,"ENCODER"  ' change display
lcdout $fe,$C0, DEC5 enc_counter
INTCON = %10001000      ' Enable PortB Change Interupts  


'************************** TESTING ROUTINES HERE **************************
test:
            if  enc_counter <> enc_counter_old then 'see if value has changed
                enc_counter_old = enc_counter		'move new value to old
           
             ' Here is were I struggle.....
             '*********************************************************************************
                lcdout $fe,$C0, SDEC2 enc_counter/10, ".", SDEC2 enc_counter//10     	'display enc_counter value
             '*********************************************************************************

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

Thank you in advance,

cbrun17