Programmable Counter Array (PCA)
The Programmable Counter Array is a special 16-bit Timer that has two 16-bit
capture/compare modules associated with it. Each of the modules can be programmed to
operate in one of four modes:
z
z
z
z
rising and/or falling edge capture (calculator of duty length for high/low pulse)
software timer
high-speed output
pulse width modulator
Each module has a pin associated with it in port 3. Module-0 is connected to pin P3.7,
module-1 to pin P3.5.
The PCA timer is a common time base for all two modules, and can be programmed to run at
1/12 the oscillator frequency, 1/2 the oscillator frequency, the Timer-0 overflow or the input on
pin ECI (P3.4). The timer count source is determined from CPS1 and CPS0 bits in the SFR
CMOD.
Module-0
Capture/Compare
P3.7/CEX0
16 Bit
Register
PCA
Timer/Counter
Module-1
Capture/Compare
Register
P3.5/CEX1
Programmable Counter Array
In the CMOD SFR, there are two additional bits associated with the PCA. On of them is CIDL
which determines if to stop the PCA while the MCU is put under idle. The other bit is ECF
which controls if to pass the interrupt from PCA into the MCU.
The CCON SFR contains the run control bit for PCA and several flags for the PCA timer and
each module. To start the PCA counting, the CR bit (CCON.6) must be set by software;
oppositely, clearing bit CR will shut off the PCA. There is a bit named CF in SFR CCON. The
CF bit (CCON.7) will be set when the PCA timer overflows, and an interrupt will be generated
if the ECF (CMOD.0) is set. The CF bit can only be cleared by software. There are two bits
38
MPC82x52A Data Sheet
MEGAWIN
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