T89C51AC2-RLSI-M datasheet(74/117 Pages) ATMEL

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Draft.A - March 30, 2001

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T89C51AC2

15. Programmable Counter Array PCA

15.1. Introduction

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 of the following signals:

• PCA clock frequency / 6

• PCA clock frequency / 2

• 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 trailing edge capture,

• software timer,

• high-speed output,

• pulse width modulator.

Module 4 can also be programmed as a watchdog timer. see Section "PCA Watchdog Timer".

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 9). 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:

• 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

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

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