Texas Instruments MSC1210 manual Example of PWM Tone Generation, 3. Statement Explanations

PWM Generator

11.3.1 Example of PWM Tone Generation

Table 11−2 illustrates configuring the PWM for tone generation, and

Table 11−3 explains selected statements.

Table 11−2. Configuring the PWM for Tone Generation

Stmt	‘C’ Source Code	Assembly Source Code
1	// PWM	PUBLIC main
		RSEG ???main?PWM
2	#include <reg1210.h>
3	#define OneUsConst (2−1)
4	sbit p33=p3^3;
5	void main(void)	Main:
6	{
7	PDCON &= 0xED; // turn on tone gen & sys timer	ANL PDCON,#0Edh
8	USEC = OneUsConst;	MOV USEC,#01h
9	P33 = 1; // turn on P3.3	SETB p33
10	PWMCON = 0; // select PWMPeriod	MOV PWMCON,#00h
11	PWM = 5; // Set PWMPeriod	MOV PWMHI,#00h
		MOV PWMLOW,#05h
12	PWMCON = 0x10; // select PWMDuty	MOV PWMCON,#10h
13	PWM = 4; // Set PWMDuty	MOV PWMHI,#00h
		MOV PWMLOW,#04h
14	PWMCON = 0x09; // Enable PWM	MOV PWMCON,#09h
15	While(1) {}	SJMP $
16	}

Table 11−3. Statement Explanations

Statement # Explanation

7ANDing PDCON with EDH effectively turns off bits 1 (PDST) and 4 (PDPWM). Clearing the PDST (Power Down System Timer) bit turns the system timer on, while clearing the PDPWM (Power Down PWM module) bit turns the PWM module on.

8Sets the USEC SFR to define 1∝s, which will be used for determining the PWM timing.

9P3.3 must be set to 1 prior to using PWM or tone generator. If P3.3 is clear, the PWM or tone generator will not produce any output.

10Clearing bit 4 by setting PWMCON to 0 selects the PWM Period register, which will be written to in the next statement.

11Having selected PWM Period in statement 10, this statement sets the PWM Period to 5.

12Setting bit 4 by setting PWMCON to 10H select the PWM Duty register will be written to in the next statement.

13Having selected PWM Duty in statement 12, this statement sets the PWM Duty to 4.

14This statements enables the PWM.

11-8