Explanation of a PWM Code

[Help]

Hi,

Anyone can help me to explain the code?

void PWM_3_Set_050(void)
   {
   T2CON &= 0xFD;   // Clear *only* C /T2 bit
   T2MOD |= 0x02;   // Set T2OE bit  (omit in basic 8052 clone)
  
   // Set at lowest frequency (~45Hz with 12MHz xtal)
   // - adjust as required (see PRM HARDWARE)
   TL2     = 0x00;   // Timer 2 low byte
   TH2     = 0x00;   // Timer 2 high byte
   RCAP2L  = 0x00;   // Timer 2 reload capture register, low byte
   RCAP2H  = 0x00;   // Timer 2 reload capture register, high byte

   ET2   = 0; // No interrupt.

   TR2   = 1; // Start timer 2
   }

How does it work? What's the program doing? How can it generate the frequency at P1^0? I try to changed it to P2^1 but still generated at P1^0..why?

Thank You.

 

[bunalmis]

pwm servomotor 4mhz

This routines initiliaze the pwm registers of MCU.

You must lean the hardware pwm unit of MCU, If you want to learn what does this codes.

 

[yager]

Re: PWM Code Explanation

It used Timer2 in Clock-Out Mode, not PWM unit in MCU. (standard 8052 has not this feature)
The T2OE & TR2 must be set to 1, the C/T2 has to be 0 for P1.0 (T2) as clock out.
its frequency = osc / ( 4 * (65536 - RCAP2) )
For more details, please refer to Intel's MCS(R) 51 Microcontroller Family User's Manual
BTW, its duty cycle is always 50%.

 

[Help]

Re: PWM Code Explanation

Hi,

Osc Freq. = 11.059Mhz

Clock-Out Freq. (Theoretical) = (Osc Freq.) / (4*65536) = 42.1867Hz

Clock-Out Freq. (Practical) = 1 / 23.7mSec = 42.1941Hz

am i rite?

So, the clock-out freq. depends on the osc freq. If i'm using 11.059MHz then i only can get 42.19Hz clock generator, rite?

 

[yager]

Re: PWM Code Explanation

Osc Freq. = 11.059Mhz
Clock-Out Freq. (Theoretical) = (Osc Freq.) / (4*65536) = 42.1867Hz
Clock-Out Freq. (Practical) = 1 / 23.7mSec = 42.1941Hz
am i rite?
So, the clock-out freq. depends on the osc freq. If i'm using 11.059MHz then i only can get 42.19Hz clock generator, rite?

You can get 42.1867Hz ~ 2.7648MHz which depends on the osc freq. and value of RCAP2 (H,L).

 

[sci-3d]

Re: PWM Code Explanation

See this for an article related PWM:

https://mcu-programming.blogspot.com/2006/09/servo-motor-control.html

 

[Help]

Re: PWM Code Explanation

Hi,

May i know what's the alternate functions for P1.0? from the AT89C52 datasheet, there say "....has two alternate function. It can be programmed to input the external clock for Timer/Counter 2 or to output a 50% duty cycle clock...".
What does it mean? What's the 2nd function is it and how it works?

Thank You.

 

[budhy]

Re: PWM Code Explanation

..... to output a 50% duty cycle clock...".
What does it mean? What's the 2nd function is it and how it works?

Its mean : you can output pre program frequency clock output on T2 pin (=P1.0)

The code at your first post do that, it generate 45 Hz (12 MHz Xtal freq) clock on T2

Please take a look at this diagram:

 

[Help]

Re: PWM Code Explanation

Hi,

How bout "input the external clock for Timer/Counter 2"? How to do the setting on the code and how can i play on it?

Thank You.

 

[budhy]

Re: PWM Code Explanation

Programmable Clock Out
A 50% duty cycle clock can be programmed to come out on P1.0, as shown in Figure 5. This pin, besides being a regular I/O pin, has two alternate functions. It can be programmed to input the external clock for Timer/Counter 2 or to output a 50% duty cycle clock ranging from 61 Hz to 4 MHz at a 16 MHz operating frequency.

To configure the Timer/Counter 2 as a clock generator, bit C/T2 (T2CON.1) must be cleared and bit T2OE (T2MOD.1) must be set. Bit TR2 (T2CON.2) starts and stops the timer. The clock-out frequency depends on the oscillator frequency and the reload value of Timer 2 capture registers (RCAP2H, RCAP2L), as shown in the following equation.

In the clock-out mode, Timer 2 roll-overs will not generate an interrupt. This behavior is similar to when Timer 2 is used as a baud-rate generator. It is possible to use Timer 2 as a baud-rate generator and a clock generator simultaneously. Note, however, that the baud-rate and clock-out frequencies cannot be determined independently from one another since they both use RCAP2H and RCAP2L.

 

[Help]

Re: PWM Code Explanation

Hi,

Thank for you info. This all info we can get from datasheet. I go through this info already but not really understood.

From my first post the code setting...

   T2CON &= 0xFD;   // Clear *only* C /T2 bit
   T2MOD |= 0x02;   // Set T2OE bit  (omit in basic 8052 clone)

Is it the Timer/Counter 2 and the clock-out setting is the same? How does it work actually? Please can you make me clear on it? again... How to do the setting on the code and how can i play on it?

Thank You.

 

[IanP]

Re: PWM Code Explanation

You use Timer 2 in Clock-Out mode when two SFR bits are configured as follows:
C/T2 = 0
T2OE = 1
The first condition can be done by writing FDh to T2CON, the second by writing 02h to T2MOD .

If you want to "PLAY" with frequency on pin P1.0 "PLAY" with these two reload bytes:
RCAP2H and RCAP2L ..

Regards,
IanP

 

[budhy]

Re: PWM Code Explanation

Your Code generate clock on T2 pin only, no other purpose!

Is it the Timer/Counter 2 and the clock-out setting is the same? How it work actually?

No, they are different, refer to Figure 1 on datasheet for Counter 2 with external Clock Source (injected to T2 pin), and figure 5 is Timer2 as clock generator configuration.

How to do the setting on the code and how can i play on it?

What do you want to do?
Counter 2 with external Clock Source
or
Clock Generator?


Do you have PATTERNS FOR TIME-TRIGGERED EMBEDDED SYSTEMS by Michael J. Pont , or the CD of that book?

 

[Help]

Re: PWM Code Explanation

Hi,

I think we already discuss the Clock-Generator(ClockOut) in our previous post..

So, how bout Counter 2 with external Clock Source? Please can you guide?

Thank You.

I dont have this book..but i got the sample codes for this book also downloaded from here...

 

[budhy]

Re: PWM Code Explanation

Setup Counter 2 with external Clock Source :

Set Timer2 operate on 16-Bit Auto-Reload or 16-Bit Capture mode (Tabel 3)
Clear T2OE = 0
Set C/T2 = 1 (Figure 1)
Set TR2 = 1 (start timer)

 

[Help]

Re: PWM Code Explanation

Setup Counter 2 with external Clock Source :

Set Timer2 operate on 16-Bit Auto-Reload or 16-Bit Capture mode (Tabel 3)
Clear T2OE = 0
Set C/T2 = 1 (Figure 1)
Set TR2 = 1 (start timer)

Hi,

How to do the setting for Timer2 operate on 16-Bit Auto-Reload or 16-Bit Capture mode ?

Actually how it work? how to control the T2 pin signal? I only know to control the T2EX for T2 Interrupt.

void CounterII(void)
   {

   T2CON &= 0xFF;   // Set C bit
   T2MOD |= 0x00;   // Clear T2OE bit  
 
   TR2   = 0; // The timer should be turned off(clear TR2) before accessing the T2 or RCAP2 registers.


   TL2     = 0xf0;   // Timer 2 low byte
   TH2     = 0xff;   // Timer 2 high byte
   RCAP2L  = 0xf0;   // Timer 2 reload capture register, low byte
   RCAP2H  = 0xff;   // Timer 2 reload capture register, high byte


   ET2   = 1; // T2 interrupt.
   EA    = 1; // Globally enable interrupts

   EXEN2 = 1;
   RCLK  = 1;

   TR2   = 1; // Start timer 2

   }

Please help me to check my code!

Thank You.

 

[Ravinder kalsi]

Re: PWM Code Explanation

I am having similar problem with clock out mode, which i just want to check. I did the coding in Keil uvision3 and upon running the program the P1.0 is not toggling .I am also attaching the code.