T89C51RD2-3CWC-L datasheet(22/86 Pages) ATMEL

22 / 86 page

Rev. F - 15 February, 2001

T89C51RD2

6.5. 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 31).

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.

The PCA timer is a common time base for all five modules (See Figure 7). The timer count source is determined

from the CPS1 and CPS0 bits in the CMOD SFR (See Table 7) 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)

PCA component

External I/O Pin

16-bit Counter

P1.2 / ECI

16-bit Module 0

P1.3 / CEX0

16-bit Module 1

P1.4 / CEX1

16-bit Module 2

P1.5 / CEX2

16-bit Module 3

P1.6 / CEX3

16-bit Module 4

P1.7 / CEX4

T89C51RD2-3CWC-L 数据表(PDF) 22 Page - ATMEL Corporation

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