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Taqoz Reloaded v2.8 - Reading a quadrature encoder — Parallax Forums

Taqoz Reloaded v2.8 - Reading a quadrature encoder

bob_g4bbybob_g4bby Posts: 394
edited 2022-07-22 11:13 in Forth

This code is adapted from an example in Jon Titus's paper on Smartpin Programming. There are two demos:-
1. Run SPEEDTEST to display the current quadrature encoder speed over a 1s period
2. Run POSTEST to display the absolute position of the quadrature encoder
The two demos assume the encoder signals are connected to Smartpin 8 and 9, so edit that to suit your setup. Both demos terminate when a key is pressed. Here's the code:-

--- Quadrature encoder driver ver 3 - for Taqoz Reloaded ver 2.8 Bob Edwards July 2022
--- NB check the assembler P2ASM is loaded before loading this code
--- This is adapted from source code in Jon Titus's paper on Smartpin Programming

pub *QUADENC* ." Quadrature Encoder reader for Taqoz Reloaded v2.8" ;

%0000_0001_000_00000_00000000_00_01011_0 := qesetup
8 := qeaddr                         --- encoder attached to smartpins 8,9, edit to suit

--- set up quadrature encoder to measure encoder pulses during 'period' clock pulses
--- if P2 clock is 20MHz, for 1 sec measurement, set period = 20,000,000
--- encoder signals are assumed connected to smartpins pin and pin+1
code QE!        ( period pin -- )
    dirl a                          --- hold the smartpin in reset
    wrpin #qesetup,a                --- set the two pins for quadrature encoder mode
    wxpin b,a                       --- set the period expressed as system clocks
    dirh a                          --- and release the smartpin to run
    jmp #@2DROP

--- Read the n pulses that occurred during the last measurement period
code QESPEED    ( pin -- n )
.l1 testp a wc                      --- test carry at the pin
    if_nc jmp #l1                   --- wait until carry detected, measurement period is over
    _ret_ rqpin a,a                 --- return the quadrature encoder pulse result

--- Display the quadrature encoder speed result until key pressed
pub SPEEDTEST   ( -- )
    20000000 qeaddr QE!             --- encode connected to pin 8,9, measuring for 1s
        qeaddr QESPEED . CRLF       --- measure pulses and display result
        100 ms
    KEY UNTIL                       --- until any key is pressed

--- Read the absolute position of the quadrature encoder
code QEPOS      ( pin -- n )
    _ret_ rqpin a,a                 --- read the accumulated counts since last read

--- Display the quadrature encoder position until a key is pressed
pub POSTEST     ( -- )
    0 qeaddr QE!                    --- setup encoder on smartpin 8,9 for position mode
        qeaddr QEPOS                --- read the encoder
        . CRLF                      --- and display the position

That's it - these words should allow you to control as many encoders as you have spare pins.

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