AT80C51RA2 データシートの表示（PDF） - Atmel Corporation
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AT80C51RA2 Datasheet PDF : 86 Pages
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6.3 Programmable Counter Array PCA
The PCA provides more timing capabilities with less CPU intervention than the standard
timer/counters. Its advantages include reduced software overhead and improved accuracy. 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 one of the following
signals:
• Oscillator frequency ÷ 12 (÷ 6 in X2 mode)
• Oscillator frequency ÷ 4 (÷ 2 in X2 mode)
• Timer 0 overflow
• External input on ECI (P1.2)
Each compare/capture modules can be programmed in any one of the following modes:
• rising and/or falling edge capture,
• software timer,
• high-speed output, or
• pulse width modulator.
Module 4 can also be programmed as a watchdog timer (See Section "PCA Watchdog Timer",
page 33).
When the compare/capture modules are programmed in the 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/O. These pins
are listed below. If the port is not used for the PCA, it can still be used for standard I/O.
PCA component
16-bit Counter
16-bit Module 0
16-bit Module 1
16-bit Module 2
16-bit Module 3
16-bit Module 4
External I/O Pin
P1.2 / ECI
P1.3 / CEX0
P1.4 / CEX1
P1.5 / CEX2
P1.6 / CEX3
P1.7 / CEX4
The PCA timer is a common time base for all five modules (See Figure 6-4). The timer count
source is determined from the CPS1 and CPS0 bits in the CMOD SFR (See Table 6-4) and can
be programmed to run at:
• 1/12 the oscillator frequency. (Or 1/6 in X2 Mode)
• 1/4 the oscillator frequency. (Or 1/2 in X2 Mode)
• The Timer 0 overflow
• The input on the ECI pin (P1.2)
24 AT/TS8xC51Rx2
4188F–8051–01/08
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