Hi, I am using 827 processor for my application. Core freq is 80Mhz so peripheral freq is 40Mhz. I want to generate PWM (under variable freq PWM mode) of 10 Hz frq and 1.5 mili seconds [Pulse width]. Here are the calculation for the same. If I use prescaler of 64 then : 40Mhz/64 = 625000 Hz i.e. 0.0000016 seconds for 1 cnt. Now If I want to generate freq of 10 hz ie. 1/10 = 0.1 seconds then value which I suppose to load in CMP1 register is .1/0.0000016 = 62500 ie. 0xf424. Please correct if I am wrong. Could anyone tell me calculation about pulse width which I suppose to load in CMP2 register? Or I will have to load same number. Is there any other way to get the respective number to get desired pulse width? Thanks and Regards, Nitin Yewale. 
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Calculation for PWM using 827
Started by ●September 9, 2002
Posted by ●September 9, 2002
The PWM prescaler only allows you to divide the IPbus by 1, 2, 4, or 8 using the PRSC0 and PRSC1 bits in the PWM Control Register (PWMCTL). Also, the PWM Counter Modulo Register (PWMCM) is only 15 bits long, with a maximum value of 32767. So, the lowest frequency is 40MHz / (8 * 32767), or about 152.6Hz. I would suggest using one of the onchip Timers for this purpose, as they have a PWM capability (see "FixedFrequency PWM Mode" in the User's Manual), their prescaler is up to fIPbus/128, and they are full 16bit counters (ie a modulo of 65536). Regards, Art Johnson Senior Systems Analyst PMC Prime Mover Controls Inc. 3600 Gilmore Way Burnaby, B.C., Canada V5G 4R8 Phone: 604 4334644 FAX: 604 4335570 Email: http://www.pmccontrols.com Original Message From: Nitin Madhukar Yewale [mailto:] Sent: Sunday, September 08, 2002 8:14 PM To: Motoroladsp Subject: [motoroladsp] Calculation for PWM using 827 Hi, I am using 827 processor for my application. Core freq is 80Mhz so peripheral freq is 40Mhz. I want to generate PWM (under variable freq PWM mode) of 10 Hz frq and 1.5 mili seconds [Pulse width]. Here are the calculation for the same. If I use prescaler of 64 then : 40Mhz/64 = 625000 Hz i.e. 0.0000016 seconds for 1 cnt. Now If I want to generate freq of 10 hz ie. 1/10 = 0.1 seconds then value which I suppose to load in CMP1 register is .1/0.0000016 = 62500 ie. 0xf424. Please correct if I am wrong. Could anyone tell me calculation about pulse width which I suppose to load in CMP2 register? Or I will have to load same number. Is there any other way to get the respective number to get desired pulse width? Thanks and Regards, Nitin Yewale. _____________________________________ Note: If you do a simple "reply" with your email client, only the author of this message will receive your answer. You need to do a "reply all" if you want your answer to be distributed to the entire group. _____________________________________ About this discussion group: To Join: To Post: To Leave: Archives: http://www.yahoogroups.com/group/motoroladsp More Groups: http://www.dsprelated.com/groups.php3 ">http://docs.yahoo.com/info/terms/ 
Posted by ●September 9, 2002
The PWM prescaler only allows you to divide the IPbus by 1, 2, 4, or 8 using the PRSC0 and PRSC1 bits in the PWM Control Register (PWMCTL). Also, the PWM Counter Modulo Register (PWMCM) is only 15 bits long, with a maximum value of 32767. So, the lowest frequency is 40MHz / (8 * 32767), or about 152.6Hz. I would suggest using one of the onchip Timers for this purpose, as they have a PWM capability (see "FixedFrequency PWM Mode" in the User's Manual), their prescaler is up to fIPbus/128, and they are full 16bit counters (ie a modulo of 65536). Regards, Art Johnson Senior Systems Analyst PMC Prime Mover Controls Inc. 3600 Gilmore Way Burnaby, B.C., Canada V5G 4R8 Phone: 604 4334644 FAX: 604 4335570 Email: http://www.pmccontrols.com Original Message From: Nitin Madhukar Yewale [mailto:] Sent: Sunday, September 08, 2002 8:14 PM To: Motoroladsp Subject: [motoroladsp] Calculation for PWM using 827 Hi, I am using 827 processor for my application. Core freq is 80Mhz so peripheral freq is 40Mhz. I want to generate PWM (under variable freq PWM mode) of 10 Hz frq and 1.5 mili seconds [Pulse width]. Here are the calculation for the same. If I use prescaler of 64 then : 40Mhz/64 = 625000 Hz i.e. 0.0000016 seconds for 1 cnt. Now If I want to generate freq of 10 hz ie. 1/10 = 0.1 seconds then value which I suppose to load in CMP1 register is .1/0.0000016 = 62500 ie. 0xf424. Please correct if I am wrong. Could anyone tell me calculation about pulse width which I suppose to load in CMP2 register? Or I will have to load same number. Is there any other way to get the respective number to get desired pulse width? Thanks and Regards, Nitin Yewale. _____________________________________ Note: If you do a simple "reply" with your email client, only the author of this message will receive your answer. You need to do a "reply all" if you want your answer to be distributed to the entire group. _____________________________________ About this discussion group: To Join: To Post: To Leave: Archives: http://www.yahoogroups.com/group/motoroladsp More Groups: http://www.dsprelated.com/groups.php3 ">http://docs.yahoo.com/info/terms/ 
Posted by ●September 9, 2002
Hi, I am using 827 processor for my application. Core freq is 80Mhz so peripheral freq is 40Mhz. I want to generate PWM (under variable freq PWM mode) of 10 Hz frq and 1.5 mili seconds [Pulse width]. Here are the calculation for the same. If I use prescaler of 64 then : 40Mhz/64 = 625000 Hz i.e. 0.0000016 seconds for 1 cnt. Now If I want to generate freq of 10 hz ie. 1/10 = 0.1 seconds then value which I suppose to load in CMP1 register is .1/0.0000016 = 62500 ie. 0xf424. Please correct if I am wrong. Could anyone tell me calculation about pulse width which I suppose to load in CMP2 register? Or I will have to load same number. Is there any other way to get the respective number to get desired pulse width? Thanks and Regards, Nitin Yewale. 
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