AN2839 Freescale Semiconductor / Motorola, AN2839 Datasheet - Page 11

• Manufacturer Part Number: AN2839
• Description: Implementing a Lamp Dimmer with an HC908Q Family MCU
• Manufacturer: Freescale Semiconductor / Motorola

Lamp Timer Source Code
Figure 10
The code starts by initializing configuration and timer registers, defining ports, and clearing variables and
accumulators.
PTA0 senses the zero-crossing detection circuit. Each time a positive or negative edge is detected the
timer starts to count until the timer modulus value (composed by TMODH:TMODL ) is reached. When a
timer overflow occurs, PTA1 generates a pulse triggering the triac.
Freescale Semiconductor
shows the flowchart for a lamp timer.
Decrement Timer
Increment Timer
Implementing a Lamp Dimmer with an HC908Q Family MCU, Rev. 0
Figure 9. Flowchart for Lamp Dimmer Source Code
Y
Y
Timer Value
Timer Value
< Upper
> Lower
Limit?
Limit?
N
N
Y
Y
Initialize Timer Module
Maximum Brightness
Turns on Lamp with
MCU Initialization
Clear Variables
PTA5 = 0?
PTA4 = 0?
Start
N
Software Description
N
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