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cfernandez
Joined: 18 Oct 2003
Posts: 145
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| PWM Question |
 Posted: Wed Feb 21, 2007 4:57 pm |
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Hi,
I need to obtain the max frecuency in PWM, I see a answer from PCM Programmer, and say:
http://www.ccsinfo.com/forum/viewtopic.php?t=17993
| Code: | The frequency calculation goes like this:
C�digo:
Crystal Frequency
PWM Freq = -----------------------------------------
(PR2 + 1) * (Timer2 Prescaler) * 4
The Timer2 prescaler can have values of 1, 4, or 16.
PR2 can have a value from 0 to 255.
So the lowest PWM frequency for your application would be:
C�digo:
24 MHz 24,000,000
----------------------- = --------------- = 1465 Hz
(255 + 1) * 16 * 4 16,384
Here is a test program for this:
(I don't have a 16c745 to test, so I'm putting in the
likely fuse values that I think you would use).
C�digo:
#include <16c745.h>
#fuses H4, NOWDT, NOPROTECT, PUT // H4 = use x4 PLL mode
#use Delay(clock=24000000)
main()
{
output_low(PIN_C2); // Set CCP1 output low
setup_ccp1(CCP_PWM); // Configure CCP1 as a PWM
setup_timer_2(T2_DIV_BY_16, 255, 1); // Setup for 1465 Hz
set_pwm1_duty(128); // 50% duty cycle
while(1); // Prevent PIC from going to sleep
} |
My PIC18F4620 work to 25Mhz, and for this the equation is:
25000000/0+1*1*4=6,25Mhz
for this my code is:
| Code: | #use fast_io (C)
#use fast_io (D)
set_tris_c( 0 );
set_tris_d( 0 );
setup_ccp1(CCP_PWM);
set_pwm1_duty(1);
setup_timer_2(T2_DIV_BY_1,0,1); |
But not work!!, the max frecuency is if I replace the Period 0 by 1, 3.125Mhz.
Why not work Period in Timer2 equal to 0??????
Thank you very much!
Best Regards, |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed Feb 21, 2007 7:56 pm |
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Here is a test program that shows how to get the maximum PWM
frequency. The key point is that your duty cycle value should be
an 'int16' value, in order to get any resolution at all, when your PR2
value is very low.
The program below has a PWM frequency of 5 Mhz. It has five steps
available for the duty cycle: 0%, 25%, 50%, 75%, and 100%.
When you increase the PWM frequency up to a very high value, the
tradeoff is that you have very low resolution (only five steps).
The program below will put out PWM pulses for each duty cycle
for one second each. Then it repeats.
| Code: |
#include <16F877.H>
#fuses HS, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock=20000000)
//#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
//=======================
void main()
{
int16 duty;
setup_timer_2(T2_DIV_BY_1, 0,1);
setup_ccp1(CCP_PWM);
while(1)
{
duty = 0; // 0% duty cycle
set_pwm1_duty(duty);
delay_ms(1000);
duty = 1; // 25% duty cycle
set_pwm1_duty(duty);
delay_ms(1000);
duty = 2; // 50% duty cycle
set_pwm1_duty(duty);
delay_ms(1000);
duty = 3; // 75% duty cycle
set_pwm1_duty(duty);
delay_ms(1000);
duty = 4; // 100% duty cycle
set_pwm1_duty(duty);
delay_ms(1000);
}
}
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cfernandez
Joined: 18 Oct 2003
Posts: 145
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| Posted: Thu Feb 22, 2007 7:45 am |
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Dear PCM Programmer!
I test your code and not work, I use 18F4620 to 25Mhz. This is the .LST. What is wrong????????
| Code: | CCS PCH C Compiler, Version 4.025, 37009 22-Feb-07 10:41
Filename: C:\Clock Generate\test.lst
ROM used: 394 bytes (1%)
Largest free fragment is 65142
RAM used: 8 (0%) at main() level
9 (0%) worst case
Stack: 1 locations
*
00000: GOTO 002C
.................... #include <18F4620>
.................... //////// Standard Header file for the PIC18F4620 device ////////////////
.................... #device PIC18F4620
.................... #list
....................
.................... #fuses HS, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
.................... #use delay(clock=25000000)
00004: CLRF FEA
00006: MOVLW 09
00008: MOVWF FE9
0000A: MOVF FEF,W
0000C: BZ 002A
0000E: MOVLW 08
00010: MOVWF 01
00012: CLRF 00
00014: DECFSZ 00,F
00016: BRA 0014
00018: DECFSZ 01,F
0001A: BRA 0012
0001C: MOVLW 19
0001E: MOVWF 00
00020: DECFSZ 00,F
00022: BRA 0020
00024: BRA 0026
00026: DECFSZ FEF,F
00028: BRA 000E
0002A: RETLW 00
.................... //#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
....................
.................... //=======================
.................... void main()
.................... {
0002C: CLRF FF8
0002E: BCF FD0.7
00030: CLRF FEA
00032: CLRF FE9
00034: MOVF FC1,W
00036: ANDLW C0
00038: IORLW 0F
0003A: MOVWF FC1
0003C: MOVLW 07
0003E: MOVWF FB4
.................... int16 duty;
....................
.................... setup_timer_2(T2_DIV_BY_1, 0,1);
00040: MOVLW 00
00042: IORLW 04
00044: MOVWF FCA
00046: MOVLW 00
00048: MOVWF FCB
.................... setup_ccp1(CCP_PWM);
0004A: MOVLW B7
0004C: ANDWF FB1,F
0004E: BCF F94.2
00050: BCF F8B.2
00052: MOVLW 0C
00054: MOVWF FBD
00056: CLRF FB7
00058: BTFSS FCA.2
0005A: BRA 0062
0005C: BCF F9E.1
0005E: BTFSS F9E.1
00060: BRA 005E
00062: BCF F94.2
00064: BCF F8B.2
....................
.................... while(1)
.................... {
.................... duty = 0; // 0% duty cycle
00066: CLRF 07
00068: CLRF 06
.................... set_pwm1_duty(duty);
0006A: MOVFF 07,02
0006E: MOVFF 06,01
00072: RRCF 02,F
00074: RRCF 01,F
00076: RRCF 02,F
00078: RRCF 01,F
0007A: RRCF 02,F
0007C: MOVFF 01,FBE
00080: RRCF 02,F
00082: RRCF 02,W
00084: ANDLW 30
00086: MOVWF 00
00088: MOVF FBD,W
0008A: ANDLW CF
0008C: IORWF 00,W
0008E: MOVWF FBD
.................... delay_ms(5000);
00090: MOVLW 14
00092: MOVWF 08
00094: MOVLW FA
00096: MOVWF 09
00098: RCALL 0004
0009A: DECFSZ 08,F
0009C: BRA 0094
....................
.................... duty = 1; // 25% duty cycle
0009E: CLRF 07
000A0: MOVLW 01
000A2: MOVWF 06
.................... set_pwm1_duty(duty);
000A4: MOVFF 07,02
000A8: MOVFF 06,01
000AC: RRCF 02,F
000AE: RRCF 01,F
000B0: RRCF 02,F
000B2: RRCF 01,F
000B4: RRCF 02,F
000B6: MOVFF 01,FBE
000BA: RRCF 02,F
000BC: RRCF 02,W
000BE: ANDLW 30
000C0: MOVWF 00
000C2: MOVF FBD,W
000C4: ANDLW CF
000C6: IORWF 00,W
000C8: MOVWF FBD
.................... delay_ms(5000);
000CA: MOVLW 14
000CC: MOVWF 08
000CE: MOVLW FA
000D0: MOVWF 09
000D2: RCALL 0004
000D4: DECFSZ 08,F
000D6: BRA 00CE
....................
.................... duty = 2; // 50% duty cycle
000D8: CLRF 07
000DA: MOVLW 02
000DC: MOVWF 06
.................... set_pwm1_duty(duty);
000DE: MOVFF 07,02
000E2: MOVFF 06,01
000E6: RRCF 02,F
000E8: RRCF 01,F
000EA: RRCF 02,F
000EC: RRCF 01,F
000EE: RRCF 02,F
000F0: MOVFF 01,FBE
000F4: RRCF 02,F
000F6: RRCF 02,W
000F8: ANDLW 30
000FA: MOVWF 00
000FC: MOVF FBD,W
000FE: ANDLW CF
00100: IORWF 00,W
00102: MOVWF FBD
.................... delay_ms(5000);
00104: MOVLW 14
00106: MOVWF 08
00108: MOVLW FA
0010A: MOVWF 09
0010C: RCALL 0004
0010E: DECFSZ 08,F
00110: BRA 0108
....................
.................... duty = 3; // 75% duty cycle
00112: CLRF 07
00114: MOVLW 03
00116: MOVWF 06
.................... set_pwm1_duty(duty);
00118: MOVFF 07,02
0011C: MOVFF 06,01
00120: RRCF 02,F
00122: RRCF 01,F
00124: RRCF 02,F
00126: RRCF 01,F
00128: RRCF 02,F
0012A: MOVFF 01,FBE
0012E: RRCF 02,F
00130: RRCF 02,W
00132: ANDLW 30
00134: MOVWF 00
00136: MOVF FBD,W
00138: ANDLW CF
0013A: IORWF 00,W
0013C: MOVWF FBD
.................... delay_ms(5000);
0013E: MOVLW 14
00140: MOVWF 08
00142: MOVLW FA
00144: MOVWF 09
00146: RCALL 0004
00148: DECFSZ 08,F
0014A: BRA 0142
....................
.................... duty = 4; // 100% duty cycle
0014C: CLRF 07
0014E: MOVLW 04
00150: MOVWF 06
.................... set_pwm1_duty(duty);
00152: MOVFF 07,02
00156: MOVFF 06,01
0015A: RRCF 02,F
0015C: RRCF 01,F
0015E: RRCF 02,F
00160: RRCF 01,F
00162: RRCF 02,F
00164: MOVFF 01,FBE
00168: RRCF 02,F
0016A: RRCF 02,W
0016C: ANDLW 30
0016E: MOVWF 00
00170: MOVF FBD,W
00172: ANDLW CF
00174: IORWF 00,W
00176: MOVWF FBD
.................... delay_ms(5000);
00178: MOVLW 14
0017A: MOVWF 08
0017C: MOVLW FA
0017E: MOVWF 09
00180: RCALL 0004
00182: DECFSZ 08,F
00184: BRA 017C
.................... }
00186: BRA 0066
....................
.................... }
00188: SLEEP
Configuration Fuses:
Word 1: 0200 HS NOIESO NOFCMEN RESERVED
Word 2: 1E1E BROWNOUT NOWDT BORV21 PUT WDT32768
Word 3: 8300 CCP2C1 PBADEN NOLPT1OSC MCLR RESERVED
Word 4: 0081 STVREN NODEBUG NOLVP NOXINST RESERVED
Word 5: C00F NOPROTECT NOCPD NOCPB
Word 6: E00F NOWRT NOWRTD NOWRTC NOWRTB
Word 7: 400F NOEBTR NOEBTRB |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Feb 22, 2007 3:14 pm |
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I don't have an 18F4620. I do have an 18F4550 and I compiled the test
program for it with PCH vs. 4.025. It works OK. I'm using a 20 MHz crystal.
Do you know that your PIC works ? Have you tried making a small
test program to blink an LED ? |
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cfernandez
Joined: 18 Oct 2003
Posts: 145
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| Posted: Thu Feb 22, 2007 3:44 pm |
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I connect my scope to pin C2 and not see 6.25Mhz...
How to test your program????
Thank you very much |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Feb 22, 2007 3:47 pm |
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I tested it with my oscilloscope.
I repeat:
Do you know for sure that your PIC works ?
Have you run any other program with it ?
Have you tested it with an LED blink program ? |
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cfernandez
Joined: 18 Oct 2003
Posts: 145
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| Posted: Thu Feb 22, 2007 3:54 pm |
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sorry,
My Pic work ok, I test this code
setup_ccp1(CCP_PWM);
setup_timer_2(T2_DIV_BY_1,1,1);
set_pwm1_duty(4L);
and I see 3.1256Mhz in my scope.
I am using a CCS Ethernet Board for this test.
Any idea??? |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Feb 22, 2007 4:38 pm |
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Some revisions of the 18F4620 have a bug with the PWM. It won't
run at the highest PWM frequency. This is the reason for your problem.
Download the Errata for the A3 and A4 silicon from this web page:
http://www.microchip.com/stellent/idcplgidcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en010304
Read this section:
| Quote: |
8. Module ECCP and CCP
Clearing the PR2 register to select the fastest
period may also result in the output(s) remaining
at a logic low output level.
|
The B4 silicon errata does not list this bug, so I assume this means
that Microchip fixed it for that revision. |
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cfernandez
Joined: 18 Oct 2003
Posts: 145
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| Posted: Fri Feb 23, 2007 7:32 am |
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Dear PCM,
You are right!!!, I test with another model and now it work!!!!!!
Thank you very much!!!! |
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