18F4431 Quaduature Encoder

[Rleonard]

I am not able to set up
the Quaduature Encoder Interface
for a MicroChip 18F4431.
Any help with the set up code
would be appreciated.

Thank you in advance.

Richard

[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.

[gokulrred]

hi all...
i am starter for PIC 18F4431......
i want to interface a encoder to that...
what are the things i need to take care?

how to do?
is it like a plug and play?(i hope no)

[cncmachineguy]

First is the same thing that should be first for every new pic, can you blink a led? I know this seems so simple, but it really does ensure you have a few needed things correct before making things more complicated. After 10+ years, I still blink LEDs the first time I use a new pic.

[Charles Linquis]

I use the "Hello World" out the serial port test. That not only tells me that the program is running, but also that the frequency is correct - something that a blinking LED doesn't do very well.

[Archangel]

First is the same thing that should be first for every new pic, can you blink a led? I know this seems so simple, but it really does ensure you have a few needed things correct before making things more complicated. After 10+ years, I still blink LEDs the first time I use a new pic.

While Bert's statement might sound like just so much talk to some I vouch for his opinion especially if you are moving to 18F chips for the first few times, I had an amazingly difficult time just getting this chip to blink the LED, owing to programmer issues, config issues . . . . ( I Know, men do not HAVE ISSUES, but PICs some times do ).

[boroko]

HI All,
This explanation has been the best one that I have found concerning the use of the PCPWM. That said, there still seems to be a bit of mystery surrounding it's use, at least to me. I mapped out the formulas in Excel, but I am still having trouble getting my head around the details. I'm trying to make a generic H-bridge for low frequencies and keep running into the wall. An 18F1330 with two pots, a switch, and the FETs with drivers. One Pot is for Frequency, the other is for Duty. The switch controls if the output is pulsed DC or cycles both ways. I'm not understanding the interaction of the frequency to the Duty. I can control the Freq just fine, but it makes a mess of the duty. Currently, the application needs it to run from 3 Hz to 100Hz with control from low power to high power (~5%-95% duty). I can see that there is a dependency with the PWM resolution, but I'm not sure how to manage it. I can get the PTPER values within 0-4096, but the resolution gets out of range. I'm thinking I need to find some way to scale the Duty to the PTPER values, and adjust accordingly, but I haven't managed to make it click. Any suggestions?

'****************************************************************
'*  Name    : PCPWM_1330_H-bridge84.BAS                         *
'*  Author  : Mark Rokus                                        *
'*  Notice  : Copyright (c) 2012 Controlled Surroundings Inc.   *
'*          : All Rights Reserved                               *
'*  Date    : 6/9/2012                                          *
'*  Version : 1.0                                               *
'*  Notes   : 18F1330 to drive H bridge:                        *
'*          : (2)L6378 drivers to (4) FDP22N50N N-FETs          *
'* used PCPWM_1330_H-bridge5 to test Hardware on separate FETS
'* New rewrite using ints
'* moved switch to RB3, rewire drivers complementary
'* NOTE: Int not working, Not going into AC
'*          Freq and Duty not correct
'****************************************************************
'                            18F1330                                                             
'              ---------------------u----------------------
'    Freq    -1|RA0/AN0/INT0                  RB3/INT3/CMP1|18-   Switch      
'    Duty    -2|RA1/AN1/INT1                  RB2/INT2/CMP2|17-   Pad      
'    Pad     -3|RA4/TOCKI/AN2                 RA7/OSC1/CLKI|16-   Pad     
'    Vpp     -4|RA5/MCLR/vpp              RA6/OSC2/CLKO/AN3|15-   Pad           
'    Gnd     -5|-- VSS                                VDD++|14-   5 vdc         
'    Tx      -6|RA2/TX/CK                      RB7/PGD/PWM5|13-    PGD      
'    Rx      -7|RA3/RX/DT                      RB6/PGC/PWM4|12-    PGC      
'   Pad      -8|RB0/PWM0                           RB5/PWM3|11-   Q1/Q4 PWM      
'   Pad      -9|RB1/PWM1                           RB4/PWM2|10-   Q2/Q3 PWM        
'              |___________________________________________|

#CONFIG
    CONFIG OSC = INTIO2        ;Internal oscillator, port function on RA6 and RA7
#ENDCONFIG
DEFINE OSC 4                  ' Actually @ 2MHz 
OSCCON  = %11011100         ' INTOSC primary, 2MHz
'****** Hardware Serial Setup ***************
DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1
DEFINE HSER_CLROERR 1 ' Clear overflow automatically
DEFINE HSER_SPBRG 8   ' 57600 Baud @ 2MHz, -3.55%
SPBRGH = 0
BAUDCON.3 = 1         ' Enable 16 bit baudrate generator
'***************************************
TRISA   = %00000011          ' PortA : outputs except RA.0/RA.1= AN
TRISB   = %00001000          ' all outputs ex: RB.3 switch i/p  
INTCON    = 0                      ' 
INTCON2 = 0                     
CMCON   = 0                      ' Comparators off
clear
'**** Analog setup   ****
    ADCON1 = %00001100   ' AN0,AN1 Analog: VDD ref. RA4 & RA6 DIO
    ADCON2 = %10010001   ' Right justified, 8 Tad, Fosc/8
'***** PWM Setup ? ********************
    PTCON0 = %00001110      ' 1:1 post, Fosc/256 (1:64) pre, UpDown(...00 free)
    PTCON1 = %11000000      ' PWM Time Base timer on, Count Down      
    PWMCON0 = %00110111     ' 0-3 PWM,  complementary
    PWMCON1 = 1             ' 1:1 postscale, updates enabled, overrides sync 
    DTCON = 0               ' zero dead-time  
    PTCON1 = %10000000      ' PWM time base is ON, counts up
    FLTCONFIG = 0           ' disable fault A 
    OVDCONS      =    %00000000    ' 
'::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
    '   Variable definition
':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: 
PORTB = 0                   ' clear port latch
Fraw         var    word          ' Raw reading for Frequency
Freq         var    word        ' Frequency of PWM
Draw         var    word        ' Raw reading for Duty
Duty         Var    Word        ' Duty of PWM
Sw             var    PORTB.3        ' switch input for AC or Positive only
'************************************************
Start:
    hserout  ["1330_H-bridge83",13,10]
    pause 500    
'*************************************
PosOnly: 
    If sw = 0 then ac            ' mode check                
  ADCON0 = %00000011            ' Start conversion on AN0
    WHILE ADCON0.1=1             ' Wait for it to complete 
    WEND   
     Fraw.HighByte = ADRESH     ' get result from AN0
     Fraw.LowByte = ADRESL      '     
  ADCON0 = %00000111            ' Start conversion on AN1
    WHILE ADCON0.1=1             ' Wait for it to complete 
    WEND    
     Draw.HighByte = ADRESH     ' get result from AN1
     Draw.LowByte = ADRESL      '      
     Freq = (Fraw) max 3        ' 
     Duty = (Draw*3) max 1        '   
         PTPERH = Freq.highbyte 'load timer: Freq low byte
         PTPERL = Freq.lowbyte     ' Freq low byte
           PDC1H = Duty.HighByte  ' PWM duty on Out1
         PDC1L = Duty.LowByte
          OVDCOND = %00001000         ' enable PWM3 OUT1 (Q1/Q4 on RB5)           
        hserout ["Duty ",dec duty," PosFreq ",dec Freq]
        goto PosOnly                ' Loop 
'***************************************************************************
AC:        ' sequence for generating Alternating pulses     
PosAlt:                                'drive Positive pulse on bridge      
        If sw = 1 then posonly    ' mode check
        PIR3.4 = 0               ' reset PWM Int flag
          while PIR3.4 = 0
         OVDCOND = %00001000       ' enable PWM3 OUT1 (Q1/Q4 on RB5)
          ADCON0 = %00000011     ' Start conversion on AN1
         WHILE ADCON0.1=1      ' Wait for it to complete 
         WEND    
         Fraw.HighByte = ADRESH ' get result from AN0
        Fraw.LowByte = ADRESL  '     
        Freq = Fraw max 3           ' 
         PTPERH = Freq.highbyte  'load timer: Freq low byte
          PTPERL = Freq.lowbyte     ' Freq low byte
        wend                       ' one cycle until Int 
NegAlt:                              ' drive Negative pulse on bridge
        PIR3.4 = 0                ' reset PWM Int flag
          while PIR3.4 = 0
         OVDCOND = %00000100    ' enable PWM1 OUT2 (Q2/Q3 on RB4)               
           ADCON0 = %00000111     ' Start conversion on AN0
         WHILE ADCON0.1=1       ' Wait for it to complete 
         WEND
        Draw.HighByte = ADRESH     ' get result from AN1
         Draw.LowByte = ADRESL      '         
          Duty = (Draw) max 1        ' 
            PDC1H = Duty.HighByte  ' PWM duty on Out1
         PDC1L = Duty.LowByte
         wend                       ' one cycle until Int    
        hserout ["Duty ",dec duty," ACFreq ",dec Freq]
        goto AC                  ' Loop         
end

So I guess the question is: Can anyone explain the relationship between PTPER and PDCx in this dynamic environment in a way that I'm not seeing?
Thanks
Bo

[HenrikOlsson]

Hi,
Basically, when you change the frequency (which you do when you change the PTPER) you also change the resolution. So, if you set the duty cycle to 50% at one frequency and then change the frequency the actual dutycyle will also change.

Basically the module is counter and two comparators. When the counter starts at 0 the output is set, when it "hits" the value of the first comparator the outputs is cleared and when the counter "hits" the value of the second compartor the PWM cycle starts over. In this case the value "in" the first comparator is your PDCx (duty)and the value in the second comparator is your PTPER (period) registers.

If the counter was an 8 bit counter and you had your second comparator (PTPER) set to 255 then there would be 256 "steps" to one PWM period. If you then set the value "in" the first compartor (PDC) to 127 you'll get a 50% dutycycle because the output will be set when the counter starts at 0 and cleared when it reaches 127, the counter will then continue to 255 and start over at which point the output is again set and so on.

Now, if you change the value of the second comparator (PTPER) to say 180 there's no longer 256 "steps" to one PWM period, the counter will start over when it "hits" 180 instead of 255 - the PWM period is shorter, PWM frequency is higher. So if you keep the value "in" the first comparator (PDC) unchanged (127) the dutycycle will no longer be 50% because the output will be "on" from 0 to 127 and then off from 127 to 180 at which point the cycle starts over.

The PWM module is more complec than this, as you've noticed, but the above is a basic explanation of the interaction between PWM period and PWM dutycycle.

/Henrik.

[dmta34]

Hi all,

Does some one by any chance have a C code on this QEI module?

Thanks !!!!!!!!!!!!

[Archangel]

This is NOT a " C " forum, it is M E Labs PBASIC.