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Dale Stewart
Joined: 21 Apr 2005
Posts: 8
Location: Wollongong, AUSTRALIA
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| Help: Can't Get Function to Work for PWM |
 Posted: Fri Jul 08, 2005 10:08 pm |
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Hi
I am a newbie to PICs and learning CCS C.
My project is a small robot, and I want to write a simple function to control the speed and direction of DC motors using PWM.
The code I wrote before worked fine. However when I tried to encapsulate this code as a function to control the motors - it won't work.
I already tried using integer variables as arguments instead of constants when calling the function.
 The problem doesn't seem to be a simple logic error, but something to do with CCS C coding ???
Any thoughts are most welcome.
Here is the code - please just focus on the function prototype, call, and definition and ignore the superfluous code, as it already works otherwise and has been tested thoroughly.
| Code: |
// Motors_Main.c
//
// Date: 09 July 05
//
// Author: Dale T Stewart
//
// Purpose:
//
// The main code template for motors
//
//
// Test Notes:
//
//
// 1. Robot motors running at ~4.8V supply via Texas
// Instruments SN754410NE motor driver.
//
//
//
//
// Hardware notes:
//
// 1. Oscillator value affects frequency of PWM output
// to motors.
//
// 2. Motor direction control bits. Motors orientation and wiring
// need to be taken into consideration. See associated notes on
// Project #1.
#include <16F876A.h>
#fuses HS, NOWDT, NOPROTECT, NOLVP
#use delay( clock = 8000000 ) // 8MHz oscillator
//------------------------------------------------------------
//
// Motors Section
//
//------------------------------------------------------------
#define PERIOD 255 // 255 is maximum period?
#define POSTSCALE 1 // 1 ( fastest ) to 3 ( slowest )
// Select and define custom register names
//
#byte motors_Port_C = 7 // Select Port C address register
//----------------------------------------------------------
//
// Constants for motors speed
//
// Motor1 = RHS Motor2 = LHS
//
// SPEED Dec ~DUTY CYCLE ( % ) Relative Speed
#define SPEED_1 77 // 30 Minimum
#define SPEED_2 102 // 40 |
#define SPEED_3 128 // 50 |
#define SPEED_4 153 // 60 |
#define SPEED_5 179 // 70 |
#define SPEED_6 204 // 80 |
#define SPEED_7 230 // 90 v
#define SPEED_8 255 // 100 Maximum
//------------------------------------------------------
//
// DIRECTION - CONTROL BITS FOR MOTOR DIRECTION
//
// These depend on motors orientation and wiring.
// See associated notes on Project #1
#define FORWARD 0b01010110
#define REVERSE 0b10100110
#define TURN_LEFT 0b10010110
#define TURN_RIGHT 0b01100110
#define COAST 0b00000000
#define BRAKE_1 0b11110110
#define BRAKE_0 0b00000110
#define LEFT_FORWARD 0b01000010
#define LEFT_REVERSE 0b10000010
#define RIGHT_REVERSE 0b00100100
#define RIGHT_FORWARD 0b00010100
//------------------------------------------
//
// Motors prototype
void motors( int dir, int spd );
//**************************************************************
//
// START MAIN
//
//***********************************************************
void main()
{
//**********************************************************
//
// Motors Setup
//
//**********************************
// Motors: Setup data direction registers
//
set_tris_c( 0x00 ) ; // Set Port C data direction register to // output
//********************************
//
// Motors: Setup CCPx pins for PWM mode
//
setup_ccp1( CCP_PWM ) ; // Configure CCP1/RC2 as a PWM
setup_ccp2( CCP_PWM ) ; // Configure CCP2/RC1 as a PWM
//************************************
//
// Motors: Setup Timer2 times and frequencies
//
//
// The cycle time will be (1/clock)*4*t2div*(period+1)
// In this program clock=8000000 and period = 255 (below)
// For the three possible selections the cycle time is:
//
// (1/8000000)*4 * 1 * 256 = 128 us or 781.3 kHz
// (1/8000000)*4 * 4 * 256 = 512 us or 195.3 kHz
// (1/8000000)*4 * 16 * 256 = 2.05 ms or 488.3 Hz
setup_timer_2( T2_DIV_BY_1 , PERIOD, POSTSCALE ) ;
// End motors setup
//
//**************************************************************
while( 1 == 1 ) // Chase your tail - woof!
{
//******************************************
//
// GO FORWARD
motors( FORWARD, SPEED_7 );
} // end while
} // end main
//**********************************************************
//
// END MAIN
//
//**********************************************************
//***********************************************************
//
// Function Definitions
//
//**************************************************************
//------------------------
//
// Function: void motors( int direction, int speed )
//
// Purpose: Control motors speed & direction
//
void motors( int direction, int speed )
{
int d, s;
motors_Port_C = d ;
set_pwm1_duty( s ) ;
set_pwm2_duty( s ) ;
}
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:-]
Cheers
Dale |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Jul 08, 2005 10:49 pm |
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In the function below, you're not using the passed parameters of
direction and speed. Instead, you're using a couple un-initialized
local variables for Port C and the duty cycle functions. You need
to get rid of the locals, and use your function parameters.
| Quote: |
void motors( int direction, int speed )
{
int d, s;
motors_Port_C = d ;
set_pwm1_duty( s ) ;
set_pwm2_duty( s ) ;
} |
Also, I would reduce the number of asterisk lines. To me, they distract
attention from the code. Before I looked at your code, I copied it to
MPLAB and deleted all those lines. Then I saw the problem right away. |
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Dale Stewart
Joined: 21 Apr 2005
Posts: 8
Location: Wollongong, AUSTRALIA
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| Posted: Fri Jul 08, 2005 11:12 pm |
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Hi PCM
Thanks heaps for your help and effort!
Cool - it works!
I am just learning C and am rusty on functions- it was a dumb mistake. 
Yeah I guess I do use a lot of asterisks to try and organise the code into sections - do you use another method?
:-]
Cheers
Dale |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Jul 08, 2005 11:50 pm |
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If you want to see my commenting style, you can see it in my post
near the end of this link. I separate functions with dashed lines.
http://www.ccsinfo.com/forum/viewtopic.php?t=23359
Everyone has their own style and I realize that when you're starting
out, you need more comments. My only reservation is that, for me,
using lines asterisks between lines of code is distracting. |
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