Texas Instruments MSC1210 - Manual (Page 131)

PWM Generator
11-7
Pulse Width Modulator/Tone Generator
This can be expressed in code as:
PWMCON = 0x10; // Sel PWM Duty Register
PWM = 128−1; // PWM toggle at a count of 128
PWMCON = 0x09; // Sel PWM Period access, SysClk rate, PWM mode
PWM = 512−1; // 11.0592MHz/512=21.6KHz PWM Freq, Period=512 counts
Note:
The port pin used for PWM (P3.3) must be configured as either standard
8051 or CMOS output for the tone generator/PWM to function.