18F4431 Quaduature Encoder

[HenrikOlsson]

Hi,
This works for me on 18F2431, should be the same. Don't forget to set the QEA, QEB & QEI pins to inputs.

QEICON = %00010100                      'Setup QEI, 4X mode, reset on indexpulse.

PosHigh var BYTE
PosLow var BYTE
PosTemp var BYTE

Position var WORD                       'Motor position in encoder counts.

Main:
  Gosub GetPosition
  HSEROUT [#Position,13,10]
  Pause 100
Goto Main

GetPosition:
'Since the position counter isn't double buffered we can get to situations
'where the lowbyte overflows between readings of the high and low byte. This
'is prevented by reading the high byte two times and compare the two readings.
'If they are the same then we're fine, if not re-read the registers.
  
    PosHigh = POSCNTH                       'Get high byte of counter
    PosLow = POSCNTL                        'Get low byte of counter
    PosTemp = POSCNTH                       'Get high byte again
    
    If PosHigh - PosTemp = 0 then Goto Done  'Compare, if equal we're done.
    
    PosHigh = POSCNTH                       'If not, get values again.
    PosLow = POSCNTL

Done:
    Position = PosHigh * 256 + PosLow       'Put high and lowbyte together.
RETURN

/Henrik Olsson.

[Rleonard]

Henrik,
Thank you for the code sample

[Rleonard]

Henrik,
The problem was that I did not set
the ANSEL0 register to digital i/o.

Great tip on counter overflow.
I will definately incorporate.

Thank You again.
Richard

[Bruce]

Isn't that an awesome controller? The motion feedback module with pulse width & frequency measurement is really handy.

Note: On the 28-pin version, forget using RE3 as an input. I tried, and submitted a support ticket to Microchip. Here's what I received back;

RE3 pin in PIC18F2331/2431 has been removed as a digital input. Hence, pin no. 1 of PIC18F2331/2431 can be used for MCLR/ Vpp only.

This change will be notified in a datasheet's (DS39616B.pdf) future update.

[HenrikOlsson]

Hi Bruce,
Thank you for info regarding RE3/MCLR as input.

It sure is a cool device. Using Darrel's interupt routines I managed to get motor controller for my robot working, with PID filter and all. Very fun project.

However.....I never managed to get QEI module going in velocity mode. I made a few attempts to begin with but could never quite figure it out so I went for my own velocity calcs (newPos-oldPos). Any pointers?

Thanks!
/Henrik Olsson.

[Bruce]

Hi Henrik,

I haven't messed with QEI yet, but if I do get something going, I'll port it from C to PBP and post it here.

My primary interest in this one was the new high-speed A/D, and motion feedback module for background pulse & freq measurements.

[HenrikOlsson]

Bruce,
I see. Thanks anyway!

/Henrik Olsson.