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Re: decoding quadrature encoders
Thank you Richard. I will test this and let you know the results.
Also, though the encoder is optical, I am going through a 74C14 hex Schmitt trigger with rc filtering to remove any stray noise. all cabling from the encoder is shielded. Monitoring the output results in clean square wave with fast rise and fall times.
Chris
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Re: decoding quadrature encoders
Hi Richard,
The asm change you suggested worked like a charm. I now get the correct counts!
Just had to make one other change that I hoped you could explain to me. Once I made the change to check the STATUS instead of _enc_tmp,7 bit, my counting was all backwards.
By changing the direction test from "btfsc _enc_old,7" to "btfss _enc_old,7", the issue was resolved. So basically the bit value for _enc_old,7 is set rather than clear on cw.
I can't express how grateful I am for all the help from both you and Henrik.
Here is the working code. I hope others will find this useful.
Code:'Read Quadrature Encoder and display value on LCD in .25 increments. 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 ' CCP1CON = 0 CCP2CON = 0 TRISA = %00000000 ' output ports TRISB = %11000000 ' set input and output ports TRISC = %00100000 ' output ports portB.4 = 0 portB.5 = 0 '************************ PROGRAM VARIABLES HERE *************************** symbol ledUp = portC.2 ' status led symbol ledDown = portC.3 ' status led2 symbol lcdbkl = portC.4 ' lcd pannel backlight symbol sw1 = portC.5 ' encoder switch symbol ledTest = portC.6 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 enc_dir VAR enc_old.bit7 Counter VAR word bank0 enc_SIGN VAR counter.bit15 Sign VAR BIT '*********************** 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 ;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 STATUS,Z ;if result is not zero, 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 _ledDown ;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 _ledUp ;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 INTCON = %10001000 ' Enable PortB Change Interupts LCDOUT $FE,1 'Init The LCD pause 500 'wait for LCD to start lcdout $FE,$80, "TEST ANGLE DISP " 'display splash screen LCDOUT $FE,$C0, "Initializing... " high lcdbkl ' turn on backlight '************************** SET DEFAULT SETTINGS HERE ********************** pause 2000 ' just wait a bit to read splash screen lcdout $FE,1 enc_counter = 0 ' set default encoder value enc_counter_old = 0 Counter = 0 lcdout $FE,$80, "Measurement " lcdout $FE,$C0,"TST ANGLE: " '************************** TESTING ROUTINES HERE ************************** test: If portC.5 = 0 then clearall 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 '(enc_counter */ 250)/2 Sign = Counter.15 ' Save sign Counter = ((ABS Counter) * 25) ' Degrees is now 0 to 900 If Sign THEN Counter = -Counter ' Restore sign, value is now -900 to 900 If not sign AND (-Counter > 0 or Counter < 0) then lcdout $FE,$80, "Measurement " lcdout $FE,$C0,"TST ANGLE:", "-",sdec Counter /100 , ".", sdec Counter // 100, " " else lcdout $FE,$80, "Measurement " lcdout $FE,$C0,"TST ANGLE:", " ", sdec -Counter /100 , ".", sdec -Counter // 100, " " endif low ledUp 'turn off CCW led low ledDown 'turn off CW led endif goto test ClearAll: enc_counter = 0 enc_counter_old = 0 Counter = 0 clear lcdout $FE,$80, "Measurement " lcdout $FE,$C0,"TST ANGLE:", " 0.00 " high ledtest pause 1000 low ledtest goto test @INT_RETURN
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Re: decoding quadrature encoders
Hi Richard,
The asm change you suggested worked like a charm. I now get the correct counts!
Just had to make one other change that I hoped you could explain to me. Once I made the change to check the STATUS instead of _enc_tmp,7 bit, my counting was all backwards.
By changing the direction test from "btfsc _enc_old,7" to "btfss _enc_old,7", the issue was resolved. So basically the bit value for _enc_old,7 is set rather than clear on cw.
I can't express how grateful I am for all the help from both you and Henrik.
Here is the working code. I home others will find this useful.
Code:'Read Quadrature Encoder and display value on LCD in .25 increments. 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 ' CCP1CON = 0 CCP2CON = 0 TRISA = %00000000 ' output ports TRISB = %11000000 ' set input and output ports TRISC = %00100000 ' output ports portB.4 = 0 portB.5 = 0 '************************ PROGRAM VARIABLES HERE *************************** symbol ledUp = portC.2 ' status led symbol ledDown = portC.3 ' status led2 symbol lcdbkl = portC.4 ' lcd pannel backlight symbol sw1 = portC.5 ' encoder switch symbol ledTest = portC.6 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 enc_dir VAR enc_old.bit7 Counter VAR word bank0 enc_SIGN VAR counter.bit15 Sign VAR BIT '*********************** 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 ;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 STATUS,Z ;if result is not zero, 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 _ledDown ;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 _ledUp ;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 INTCON = %10001000 ' Enable PortB Change Interupts LCDOUT $FE,1 'Init The LCD pause 500 'wait for LCD to start lcdout $FE,$80, "TEST ANGLE DISP " 'display splash screen LCDOUT $FE,$C0, "Initializing... " high lcdbkl ' turn on backlight '************************** SET DEFAULT SETTINGS HERE ********************** pause 2000 ' just wait a bit to read splash screen lcdout $FE,1 enc_counter = 0 ' set default encoder value enc_counter_old = 0 Counter = 0 lcdout $FE,$80, "Measurement " lcdout $FE,$C0,"TST ANGLE: " '************************** TESTING ROUTINES HERE ************************** test: If portC.5 = 0 then clearall 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 '(enc_counter */ 250)/2 Sign = Counter.15 ' Save sign Counter = ((ABS Counter) * 25) ' Degrees is now 0 to 900 If Sign THEN Counter = -Counter ' Restore sign, value is now -900 to 900 If not sign AND (-Counter < 0 or Counter > 0) then lcdout $FE,$80, "Measurement " lcdout $FE,$C0,"TST ANGLE:", "-",sdec Counter /100 , ".", sdec Counter // 100, " " else lcdout $FE,$80, "Measurement " lcdout $FE,$C0,"TST ANGLE:", " ", sdec -Counter /100 , ".", sdec -Counter // 100, " " endif low ledUp 'turn off CCW led low ledDown 'turn off CW led endif goto test ClearAll: enc_counter = 0 enc_counter_old = 0 Counter = 0 clear lcdout $FE,$80, "Measurement " lcdout $FE,$C0,"TST ANGLE:", " 0.00 " high ledtest pause 1000 low ledtest goto test @INT_RETURN
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Re: decoding quadrature encoders
Direction is a matter of interpretation.Just had to make one other change that I hoped you could explain to me. Once I made the change to check the STATUS instead of _enc_tmp,7 bit, my counting was all backwards.
By changing the direction test from "btfsc _enc_old,7" to "btfss _enc_old,7", the issue was resolved. So basically the bit value for _enc_old,7 is set rather than clear on cw.
changing the direction test from "btfsc _enc_old,7" to "btfss _enc_old,7 OR
changing the direction test from "btfsc _enc_old,6" to "btfsc _enc_old,6 OR
swaping the "A","B" connections ,will all cause the "direction " to reverse
I notice you are still incorrectly not saving the mcu context upon isr entry
Warning I'm not a teacher
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Re: decoding quadrature encoders
Hi Richard,
Not sure why my last post went in twice... Sorry.
When I added the mcu context save routine the display crashed. It will ~ work if I move the shaft slowly, however, moving quickly caused the code to trip over itself and lockup the screen.
My first guess was that when jumping out of the ISR, the next return in the main program uses the most recent return address on the stack and returns to the point the interrupt occurred, crashing the program.
However, I noticed my up/down LED indicators are still operational which suggests the code is still working okay and its either the formatting or calculations that are causing some latency. if I perform a display reset, the counting resumes normally.
So I made two changes which seem to have resolved the issue.
I removed the two LCD defines:
DEFINE LCD_COMMANDUS 2000 ' Set Command Delay time in uS
DEFINE LCD_DATAUS 60 ' Set Data delay time in uS
And added a 50ms pause after the display routine to give the display time to settle.
I know there must be a more efficient way to format the display to reduce the number of instructions necessary to accomplish the xx.xx by .25 increment, but this seems to smooth out he results.
Thanks again for you feedback.
Chris
Last edited by cbrun17; - 11th February 2017 at 17:37.
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Re: decoding quadrature encoders
Hi Chris,
In your test routine loop you're re-Writing alot of static text on the LCD and you're doing some "strange" things to get the correct formating. Here's an idea which probably is a bit more efficient:/Henrik.Code:' Print static information on LCD once, then leave it alone. lcdout $FE,$80, "Measurement " lcdout $FE,$C0,"TST ANGLE: " '************************** TESTING ROUTINES HERE ************************** test: If portC.5 = 0 then clearall 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) * 25) ' Degrees is now 0 to 900 ' Not doing this here, later (or not at all). 'If Sign THEN Counter = -Counter ' Restore sign, value is now -900 to 900 LCDOUT $FE, $CB 'Position cursor at 11th character on 2nd row. IF SIGN THEN LCDOUT "-" ELSE LCDOUT " " ENDIF LCDOUT DEC Counter / 100, ".", DEC Counter // 100, " " ' To save execution cycles you're better off not using HIGH/LOW low ledUp 'turn off CCW led low ledDown 'turn off CW led ' If the only purpose of the Counter variable is to display the value ' the there's no need to restore the sign of it so the following line ' could be deleted. If Sign THEN Counter = -Counter ' Restore sign, value is now -900 to 900 endif goto test
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Re: decoding quadrature encoders
Hi Henrik,
I changed the display routine as you described and it does work much better. I sure do over think some of this stuff... I did have to increase the pause to 250ms to allow for the display to update since it seemed to trip over itself a little more frequently this way.
I believe moving to either serial LCD or 7 seg LED might be the better solution.
Thanks again for your expert advise.
Chris
Last edited by cbrun17; - 11th February 2017 at 19:28.
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Re: decoding quadrature encoders
Excuse me Henrik, If you read the spec. sheet you can set the interrupt edge for the INT0 and INT1. It is not required to set it each time. Also the interrupt routine look like:
'************************************************* ********************
INC_C: 'INTERRUPT SERVICE ROUTINE FOR EXTERNAL INTERRUPT-0
'************************************************* ********************
POSITION = POSITION + 1
@ INT_RETURN
'************************************************* ********************
DEC_C: 'INTERRUPT SERVICE ROUTINE FOR EXTERNAL INTERRUPT-1
'************************************************* ********************
POSITION = POSITION - 1
@ INT_RETURN
That's all there is to it.
Dave Purola,
N8NTA
EN82fn
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Re: decoding quadrature encoders
Out of curiosity, what R/C values did you find to be optimal on your schmitt triggers?Originally Posted by cbrun17
Picster
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Re: decoding quadrature encoders
Ok, I did some trials myself and ended up with R1=100k, R2=33k, C=0.1uF working well with Schmitt trigger inputs on the PIC I'm using (see circuit attached). That's with a detented encoder, using the same values for the two rotary outputs AND the built-in pushbutton.
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Re: decoding quadrature encoders
You certainly could. Yet this works great in my application, for which I am using switch polling, not interrupts. I would imagine it also depends on the characteristics of the encoder.
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Re: decoding quadrature encoders
Of course it does. But I am worried about the input impedance of the PIC and leakage currents.
Ioannis
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Re: decoding quadrature encoders
Hey Ioannis,
I'm hoping you can shed some additional light on this for me.
I know the "design standard" is to use a 10k pullup for PIC inputs that switch to ground - which from my understanding is really not so much about leakage, but more about noise on the "antenna" that an input wire or trace can become. The internal weak pullups tend to work on a breadboard or on a PC board, as long as the system isn't subject to much electrical noise, but "guaranteeing" that environment is far from possible in real world applications. The internal "weak pullups" have equivalent impedance ranges from 200k to 16k, per PIC specs. Meanwhile, input impedance for ports works out to around 50Mohms per specs. I agree, it is always good to have a "solid" and unquestionable pull-up instead of something where spurious glitches can put you into nebulous range, particularly with an input that's NOT configured as a schmitt trigger and you can get all kinds of undefined questionable results. Absolutely makes sense to use "tried and true" 10k in these situations.
However, despite the above, part of the benefit of using a capacitor on the input (again, only with the schmitt trigger config) is that it will help to eliminate spurious noise, effectively shunting spikes to ground and only letting relatively persistent voltage levels through. Hence the reason, I believe, why these values may be demonstrated to work for a schmitt trigger input configuration. I picked these values around the 0.1uF capacitor since I have a ton of them.
Does this make sense, or am I missing something else that I should be considering?
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