decoding quadrature encoders

[ice]

Luciano,

when i try the program u recommended [12th april] as below,
there are alot of instances when the program gets confused with direction,
so it sometime increments and decrements.Im not using interrupts

when i move the motor slowly,the problem still persists.

old_val 		VAR BYTE
new_val 		VAR BYTE
direction_bit 	VAR BIT
enc_counter 	VAR WORD
adval			VAR	WORD				' Create adval to store result
potval			VAR WORD
servo_val		VAR	WORD
difference		VAR WORD
	
TRISB=%11111111
enc_counter=32500		
HPwm 0,100,20000	
    
	

	new_val = PORTB & %00000011
start:
	old_val = new_val
	
	
again:
	new_val = PORTB & %00000011
	'LCDOut $fe,1,"no move"
	IF new_val = old_val Then again

	direction_bit = old_val.bit0 ^ new_val.bit1
	
	IF direction_bit = 1 Then  
	
		LCDOut $fe,1,"Last was CW"
		enc_counter = enc_counter + 1
		LCDOut $fe,$c0,DEC enc_counter

	Else
		LCDOut $fe,1,"Last was CCW"
		enc_counter = enc_counter - 1
		LCDOut $fe,$c0,DEC enc_counter	
	
	EndIF
    	GoTo start

Thank you for your responses

[Luciano]

Hi!

I need more info.

The version of the PIC used. (16F628, 16F628A, ...).

If you are using a commercial board for the PIC, I need
the URL where I can see the board.

The brand and model number of the encoder and the URL where I can
download the data sheet.

I also need to know how you have connected the encoder to
PORTB.0 and PORTB.1. (Pull-up resistors? If yes, values).


Luciano

[ice]

Luciano,

The version of the PIC used. (16F628, 16F628A, ...).

im using the PIC16F873A

If you are using a commercial board for the PIC, I need
the URL where I can see the board.

I made my own dev board..has an LCD,A/D..the usual features..
works on a 4Mhz crystal..
The board works perfectly as i have run accelerometers,D/A converters from the same board

The brand and model number of the encoder and the URL where I can
download the data sheet.

Maxon 22578
500 counts per turn
http://www.maxonmotor.com/docsx/Down...f/05_238_e.pdf

I also need to know how you have connected the encoder to
PORTB.0 and PORTB.1. (Pull-up resistors? If yes, values).

Pull up resistors
with value 1.8K


Thanks for all your help

[ice]

ok,a little progress,
seems like i'm loosing counts ,because of the LCDout commands

if i make my code tighter[remove the LCDcommands],i am able to monitor direction ,but a bit of interference still persists.
I'm on a 4Mhz..i'll switch to a 20Mhz tomorrow and post my progress

[Luciano]

When you try the example code with the LCD, turn the encoder very slowly
with your fingers.(About 1 degree per second).The example is just to see
that the decode technique works.

For the real code you need to use the interrupt-onchange feature, and the
code has to be written in assembly otherwise you will lose encoder counts.
(Read the PicBasic Manual about interrupts in Basic and assembly).

The encoder and pull-up resistors are OK.

Luciano

[ice]

yes works beautifully at 3 degrres per second,im using PWM thru a motor driver...the decode program works well

ill have to work on the interrupts..it will take time...
is there an example or "guide" code in assembly..it's a bit confusing in assembly,.
Ill try it anyway,will keep you posted.

[Luciano]

Hello,

Probably you already know that.An interrupt in PicBasic
language will not work for the rotary encoder.
You must use an interrupt in assembly.

The assembly code for the interrupt will be simple.
In addition of what you have to save and restore
for the correct functioning of PicBasic, the assembly
code for the rotary encoder is just detect its direction
and increase or decrease the counter variable and maybe set
a flag for the direction if you need this info in the basic program.
The rest is done by the basic program once you exit the assembly
interrupt routine.

Read section 29 Instruction Set of the Mid-Range MCU Family Reference Manual.
http://ww1.microchip.com/downloads/e...Doc/33023a.pdf

To do:

Understand the differences between interrupts in PicBasic and
interrupts in assembly and understand why you need an assembly
interrupt for your rotary encoder. (PicBasic Manual).

How to declare a variable in basic and use
it in the interrupt assembly code. (Share variables
between basic and assembly, see PicBasic Manual).

Understand what you need to save and restore when
you enter and exit the assembly interrupt. (PicBasic Manual).

In PicBasic language, try first the interrupt-onchange feature.
The A/B signals of the encoder will be connected of two of
these PINs that have the interrupt-onchange feature.
(This is not the interrupt on RB0).
Once the interrupt-onchange feature works in basic then
you will be ready to implement that in assembly.

RB<7:4>, have an interrupt-onchange feature.

Four of PORTB’s pins, RB<7:4>, have an interrupt-onchange
feature. Only pins configured as inputs can
cause this interrupt to occur (i.e., any RB<7:4> pin configured
as an output is excluded from the interrupt-onchange
comparison). The input pins (of RB7:RB4) are
compared with the old value latched on the last read of
PORTB. The “mismatch” outputs of RB7:RB4 are
OR’ed together to generate the RBIF interrupt (flag
latched in INTCON<0>).

INTCON = %10001000 'Enable RBIE
INTCON.0 = 0 'Clear Port Change Interrupt Flag bit

Read section 8 of the Mid-Range MCU Family Reference Manual.
http://ww1.microchip.com/downloads/e...Doc/33023a.pdf

AN566 - Using the PORTB Interrupt on Change as an External Interrupt.
http://ww1.microchip.com/downloads/e...tes/00566b.pdf

Best regards,

Luciano

[ice]

Thanks Luciano,
Im read up the pbp manual and others for interrupts...
..however my test program isnt compiling..

		wsave 	VAR BYTE $20 system				'bank0
		wsave1 	VAR BYTE $a0 system				'bank1
		'wsave2 	VAR BYTE $120 system		'bank2
		'wsave3 	VAR BYTE $1a0 system		'bank3
		ssave 	VAR BYTE bank0 system
		psave 	VAR BYTE bank0 system
		led 	VAR PORTB.1
		
		GoTo start_0 					' Skip around interrupt handler	


		DEFINE INTLHAND myint			' DEFINE INTERRUPT handler
		Asm
myint:	bsf _led 						; Turn on LED (for example)
		bcf intcon.0
				
		retfie
		EndAsm
    
	
		
										' Assembly language INTERRUPT handler    
		

    
start_0:
		
		TRISB=%11111101	
		Low led 						' Turn LED off
		INTCON = %10001000				' Enable INTERRUPT ON PORTB.0
        
	
loop: 		GoTo loop 						' Wait here till interrupted

1> compile error "DEFINE INTHAND myint"
....undefined symbol myint
however if i relpace it with DEFINE INTLHAND myint,(which is only for th 18x series),it complies ok..

2>im using a 16F873A,which has a 4K flash,meaning 4 banks...
according to the PBP manual, i have to define wsave,wsave1,wsave2,wsave3...
it takes in wsave and wsave1...but when i declare wsave2 and wsave3..it gives a RAM_END 255 error

3>i cannot get the LED to blink either by using the int0 or the Interr On change<4:7>