Programmable Counter Array (Pca) - STC STC12C5A Series Manual

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:
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 1. Module-0 is connected to pin P1.3, module-1 to pin
P1.4.
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
16 Bit
PCA
Timer/Counter
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 named CCF0 and CCF1 in SFR CCON. The CCF0 and
CCF1 serve as flags for module-0 and module-1 respectively. They are set by hardware when either a
match or a capture occurs. These flags also can only be cleared by software.
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Programmable Counter Array
STC12C5Axx Technical Summary
CMOD.
Module-0 P1.3/CEX0/
PCA0/PWM0
Capture/Compare
Register
Module-1
P1.4/CEX1/
Capture/Compare
PCA1/PWM1
Register
45
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