Rainbow-electronics T89C51CC01 Bedienungsanleitung PDF herunterladen (Seite 108)

108

T89C51CC01

Rev. D – 17-Dec-01

16. 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 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:

• PCA clock frequency / 6 (see “clock” section)

• PCA clock frequency / 2

•Timer0overflow

• 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,

• 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.

Thesepinsarelistedbelow.IftheportisnotusedforthePCA,itcanstillbeusedfor

standard I/O.

16.1 PCA Timer The PCA timer is a common time base for all five modules (see Figure 40). 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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Rainbow-electronics T89C51CC01 Bedienungsanleitung Seite 108