PWM on the PIC16F1509 in ASM

[Edit: If you’re looking for NCO (numerically controlled oscillator) usage instead of the PWM module take a look here instead. However note the code is in C (for XC8) not ASM]

Another lazy Sunday… A lot of OT the last few weeks at work and Sunday about the only day I have for relaxation so to clear my mind I wrote some test code for Pulse Width Modulation on a development board I purchased from @TINDE made by @TAUTIC . I’ll attach the code for anyone to use.

MPLAB on the laptop with a @TAUTIC / @TINDE dev board with a PWM test output.
MPLAB on the laptop with a @TAUTIC / @TINDE dev board with a PWM test output.

The code outputs on PWM1 (RC5) at about 1Khz at just under 50% duty cycle but that easy to change if you read the Microchip 16F1508/9 spec sheet section 23.

;*******************************************************************************
;                                                                              *
;    Microchip licenses this software to you solely for use with Microchip     *
;    products. The software is owned by Microchip and/or its licensors, and is *
;    protected under applicable copyright laws.  All rights reserved.          *
;                                                                              *
;    This software and any accompanying information is for suggestion only.    *
;    It shall not be deemed to modify Microchip?s standard warranty for its    *
;    products.  It is your responsibility to ensure that this software meets   *
;    your requirements.                                                        *
;                                                                              *
;    SOFTWARE IS PROVIDED "AS IS".  MICROCHIP AND ITS LICENSORS EXPRESSLY      *
;    DISCLAIM ANY WARRANTY OF ANY KIND, WHETHER EXPRESS OR IMPLIED, INCLUDING  *
;    BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS    *
;    FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT. IN NO EVENT SHALL          *
;    MICROCHIP OR ITS LICENSORS BE LIABLE FOR ANY INCIDENTAL, SPECIAL,         *
;    INDIRECT OR CONSEQUENTIAL DAMAGES, LOST PROFITS OR LOST DATA, HARM TO     *
;    YOUR EQUIPMENT, COST OF PROCUREMENT OF SUBSTITUTE GOODS, TECHNOLOGY OR    *
;    SERVICES, ANY CLAIMS BY THIRD PARTIES (INCLUDING BUT NOT LIMITED TO ANY   *
;    DEFENSE THEREOF), ANY CLAIMS FOR INDEMNITY OR CONTRIBUTION, OR OTHER      *
;    SIMILAR COSTS.                                                            *
;                                                                              *
;    To the fullest extend allowed by law, Microchip and its licensors         *
;    liability shall not exceed the amount of fee, if any, that you have paid  *
;    directly to Microchip to use this software.                               *
;                                                                              *
;    MICROCHIP PROVIDES THIS SOFTWARE CONDITIONALLY UPON YOUR ACCEPTANCE OF    *
;    THESE TERMS.                                                              *
;                                                                              *
;*******************************************************************************
;                                                                              *
;    Filename:      main.asm                                                   *
;    Date:          Sept 29 2013                                               *
;    File Version:  1.0                                                        *
;    Author:        Charles Douvier                                            *
;    Company:                                                                  *
;    Description:   Test of PWM1                                               *
;
;    Device 16F1509
;
;
;
;
; PIN DIAGRAM
;
;   RA0                             RC0
;   RA1                             RC1
;   RA2                             RC2     STATUS LED
;                                   RC3
;   RA4             RB4             RC4
;   RA5             RB5             RC5     PWM1
;                   RB6             RC6
;                   RB7             RC7
;
;------------------------------------------------------------           *
;*******************************************************************************
;                                                                              *
;    Notes: In the MPLAB X Help, refer to the MPASM Assembler documentation    *
;    for information on assembly instructions.                                 *
;                                                                              *
;*******************************************************************************
;                                                                              *
;    Known Issues: This template is designed for relocatable code.  As such,   *
;    build errors such as "Directive only allowed when generating an object    *
;    file" will result when the 'Build in Absolute Mode' checkbox is selected  *
;    in the project properties.  Designing code in absolute mode is            *
;    antiquated - use relocatable mode.                                        *
;                                                                              *
;*******************************************************************************
;                                                                              *
;    Revision History:
;           2013-09-28  Initial                                                *
;                                                                              *
;*******************************************************************************

;*******************************************************************************
; Processor Inclusion
;
;*******************************************************************************
    errorlevel -230, -302, -303, -313
    LIST R=DEC
#include "p16f1509.inc"
;*******************************************************************************
;
; Word Setup
;
;
;*******************************************************************************
    __CONFIG _CONFIG1, _FOSC_INTOSC & _WDTE_OFF & _PWRTE_OFF & _CLKOUTEN_OFF
    __CONFIG _CONFIG2, _LVP_OFF & _STVREN_ON
;*******************************************************************************
;
;  Variable Definitions
;
;*******************************************************************************
; TODO PLACE VARIABLE DEFINITIONS GO HERE
;*******************************************************************************
; Reset Vector
;*******************************************************************************
RES_VECT  CODE    0x0000            ; processor reset vector
    GOTO    START                   ; go to beginning of program
;*******************************************************************************
; TODO INSERT ISR HERE
;*******************************************************************************
; MAIN PROGRAM
;*******************************************************************************
MAIN_PROG CODE                      ; let linker place main program
INIT:
                            ;RC5 = PWM1
    BANKSEL LATA            ;Data Latch
    CLRF LATA               ;
    BANKSEL ANSELC          ;
    CLRF ANSELC             ;Digital IO
    BANKSEL PORTC           ;
    BCF PORTC,5             ;Clear PWM1
    BANKSEL TRISC           ;Set all PORTC to outputs
    CLRF TRISC
    BANKSEL PORTC
    BSF PORTC,2
    BANKSEL OSCCON
    MOVLW   0x78            ;16MHZ Clock
    MOVWF   OSCCON
    BANKSEL PWM1CON         ;
    CLRF PWM1CON            ;Disable PWM bits
    BANKSEL PR2
    MOVLW 0xFF
    MOVWF PR2               ;Load PR2 with 0xFF
                            ;Timer/PR set up is 973Hz
    BANKSEL PWM1DCH
    CLRF PWM1DCH
    BANKSEL PWM1DCL
    CLRF PWM1DCL
    BSF PORTC,2
    BANKSEL PWM1DCH
    MOVLW   0x6F
    MOVWF   PWM1DCH

                            ;copied code, havent check this yet.
    ;ENABLE INTERRUPT
    BANKSEL PIE1
    BSF PIE1,1
    bcf        PIR1,2
                    ;-----------------------------------
                    ;Configure and start Timer2
;CONFIGURE TIMER.. copied code review.
    BANKSEL T2CON
    MOVLW B'00000110'   ;MOVLW B'00000110'
    MOVWF T2CON
                    ;Enable PWM output pin and wait until Timer2
                    ;overflows, TMR2IF bit of the PIR1 register is set.
                    ;See note below.
    btfss    PIR1,1                ;Test for T2 interrupt
    goto    $-1
                    ;Enable the PWMx pin output driver(s) by clearing
                    ;the associated TRIS bit(s) and setting the
                    ;PWMxOE bit of the PWMxCON register.
                    ;Configure the PWM module by loading the
                    ;PWMxCON register with the appropriate values.
    BANKSEL TRISC          ;Enable Outputs
    CLRF    TRISC
    BANKSEL PWM1CON        ;Enable PWM1
    MOVLW    B'11000000'
    MOVWF    PWM1CON
    RETURN
START
    CALL INIT
    BANKSEL PORTC            ;select PORTC for heatbeat
LOOP:
    BSF PORTC,2              ;heart beat
    MOVLW 0x55
    NOP                      ;future code
    BCF PORTC,2
    GOTO LOOP                ;loop forever
    END

 

 

4 Comments

  • Rahul
    October 10, 2013 - 12:56 am | Permalink

    do you have code for pic16f1503 . i got problem to generate PWM on it. will you send me code on mail where to change bits.

    • Chas
      October 10, 2013 - 4:04 pm | Permalink

      The 16F1503 is in the same family as the 16F1509. PWM1 is on RC5 on both devices… so you should be able to just change the device in the code. I don’t have a 16F1503 or I’d try it myself.

  • Nikolay Pokhilchenko
    October 25, 2013 - 10:55 am | Permalink

    If PIC have paged program memory and you’ve left the linker to place the code, you should use pagesel assembler instruction.
    In some cases, when there are another code blocks, the linker may place your Start code not on the first page. So the pagesel assembler instruction is needed to generate appropriate MOVLP PIC instruction before GOTO.

    • Chas
      October 25, 2013 - 4:54 pm | Permalink

      Nikolay,Thank you for your comment. I agree if you allow the linker to place your code it’s a good idea to PAGESEL LABEL1 and then CALL LABEL1 and on return PAGESEL $ .. This was a snippet and I felt pretty safe about it because it was way smaller than a page. Although a note might also to be add “errorlevel -312 ;no pagesel warnings” … those can get annoying.

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