XC912BC32CFU8 Motorola Semiconductor Products, XC912BC32CFU8 Datasheet - Page 166

• Manufacturer Part Number: XC912BC32CFU8
• Description: M68HC12B Family Data Sheet
• Manufacturer: Motorola Semiconductor Products

Standard Timer Module (TIM)
12.5 Using the Output Compare Function to Generate a Square Wave
12.5.1 Sample Calculation to Obtain Period Counts
12.5.2 Equipment
Data Sheet
166
This timer exercise is intended to utilize the output compare function to generate a
square wave of predetermined duty cycle and frequency.
The program generates a square wave, 50 percent duty cycle, on output
compare 2 (OC2). The signal will be measured by the HC11 on the UDLP1 board.
It assumes a 8.0 MHz operating frequency for the E clock. The control registers are
initialized to disable interrupts, configure for proper pin control action and also the
TC2H register for desired compare value. The appropiate count must be calculated
to achieve the desired frequency and duty cycle. For example: for a 50 percent
duty, 1 KHz signal each period must consist of 2048 counts or 1024 counts high
and 1024 counts low. In essence a $0400 is added to generate a frequency of
1 kHz.
The sample calculation to obtain period counts is:
For this exercise, use the M68HC912B32EVB emulation board.
•
•
Square wave frequency 1000 Hz, duty cycle 50%
For 1000 Hz frequency:
–
–
–
For a 1 KHz, 50 percent duty cycle:
–
–
E-clock = 8 MHz
IC/OC resolution factor = 1/(E-clock/Prescaler)
If the Prescaler = 4, then output compare resolution is 0.5 µs
1/F = T = 1/1000 = 1 ms
F for output compare = prescaler/E clock = 2 MHz
Standard Timer Module (TIM)
1 ms
Figure 12-30. Example Waveform
0.5 ms
NUMBER OF CLOCKS = F * D
THEREFORE,
#CLOCKS = (2 MHz) * (0.5 ms) = 1024 = $0400
M68HC12B Family — Rev. 8.0
MOTOROLA