MC68HC812A4 Datasheet, PDF (209/342 Pages) Motorola, Inc – 16-bit device composed of standard on-chip peripheral modules connected by an intermodule bus. Modules include

Standard Timer Module
Using the Output Compare Function to Generate a Square Wave
12.12 Using the Output Compare Function to Generate a Square Wave
This timer exercise is intended to utilize the output compare function to
generate a square wave of predetermined duty cycle and frequency.
Square wave frequency 1000 Hz, duty cycle 50%
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.
12.12.1 Sample Calculation to Obtain Period Counts
The sample calculation to obtain period counts is:
• For 1000 Hz frequency:
– E-clock = 8 MHz
– IC/OC resolution factor = 1/(E-clock/Prescaler)
– If the Prescaler = 4, then output compare resolution is 0.5 µs
• For a 1 KHz, 50 percent duty cycle:
– 1/F = T = 1/1000 = 1 ms
– F for output compare = prescaler/E clock = 2 MHz
Advance Information
MOTOROLA
1 ms
0.5 ms
NUMBER OF CLOCKS = F * D
THEREFORE,
#CLOCKS = (2 MHz) * (0.5 ms) = 1024 = $0400
Figure 12-28. Example Waveform
Standard Timer Module
MC68HC812A4 — Rev. 3.0
209