at89c51ac3-s3sim ATMEL Corporation, at89c51ac3-s3sim Datasheet - Page 94

• Manufacturer Part Number: at89c51ac3-s3sim
• Description: At89c51ac3 Enhanced 8-bit Microcontroller With 64kb Flash Memory
• Manufacturer: ATMEL Corporation

Programmable
Counter Array (PCA)
PCA Timer
94
AT89C51AC3
The PCA provides more timing capabilities with less CPU intervention than the standard
timer/counters. Its advantages include reduced software overhead and improved accu-
racy. The PCA consists of a dedicated timer/counter which serves as the time base for
an array of five compare/capture modules. Its clock input can be programmed to count
any of the following signals:
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Each compare/capture modules can be programmed in any one of the following modes:
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Module 4 can also be programmed as a WatchDog timer. see the "PCA WatchDog
Timer" section.
When the compare/capture modules are programmed in capture mode, software timer,
or high speed output mode, an interrupt can be generated when the module executes its
function. All five modules plus the PCA timer overflow share one interrupt vector.
The PCA timer/counter and compare/capture modules share Port 1 for external I/Os.
These pins are listed below. If the port is not used for the PCA, it can still be used for
standard I/O.
The PCA timer is a common time base for all five modules (see Figure 53). The timer
count source is determined from the CPS1 and CPS0 bits in the CMOD SFR (see Table
8) and can be programmed to run at:
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PCA clock frequency/6 (see “clock” section)
PCA clock frequency/2
Timer 0 overflow
External input on ECI (P1.2)
rising and/or falling edge capture,
software timer,
high-speed output,
pulse width modulator.
1/6 the PCA clock frequency.
1/2 the PCA clock frequency.
the Timer 0 overflow.
the input on the ECI pin (P1.2).
PCA Component
16-bit Module 0
16-bit Module 1
16-bit Module 2
16-bit Module 3
16-bit Module 4
16-bit Counter
External I/O Pin
P1.3/CEX0
P1.4/CEX1
P1.5/CEX2
P1.6/CEX3
P1.7/CEX4
P1.2/ECI
4383D–8051–02/08