AT89C51ED2-RDTIM datasheet(40/137 Pages) ATMEL

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AT89C51RD2/ED2

4235E–8051–04/04

Figure 17. PCA Interrupt System

PCA Modules: each one of the five compare/capture modules has six possible func-

tions. It can perform:

•

16-bit Capture, positive-edge triggered

•

16-bit Capture, negative-edge triggered

•

16-bit Capture, both positive and negative-edge triggered

•

16-bit Software Timer

•

16-bit High Speed Output

•

8-bit Pulse Width Modulator

In addition, Module 4 can be used as a Watchdog Timer.

Each module in the PCA has a special function register associated with it. These regis-

ters are: CCAPM0 for Module 0, CCAPM1 for Module 1, etc. (See Table 24). The

registers contain the bits that control the mode that each module will operate in.

•

The ECCF bit (CCAPMn.0 where n = 0, 1, 2, 3, or 4 depending on the module)

enables the CCF flag in the CCON SFR to generate an interrupt when a match or

compare occurs in the associated module.

•

PWM (CCAPMn.1) enables the pulse width modulation mode.

•

The TOG bit (CCAPMn.2) when set causes the CEX output associated with the

module to toggle when there is a match between the PCA counter and the modules

capture/compare register.

•

The match bit MAT (CCAPMn.3) when set will cause the CCFn bit in the CCON

capture/compare register.

•

The next two bits CAPN (CCAPMn.4) and CAPP (CCAPMn.5) determine the edge

that a capture input will be active on. The CAPN bit enables the negative edge, and

the CAPP bit enables the positive edge. If both bits are set both edges will be

enabled and a capture will occur for either transition.

•

The last bit in the register ECOM (CCAPMn.6) when set enables the comparator

function.

CCON

0xD8

CCF4 CCF3

CCF2

CCF1

CCF0

Module 4

Module 3

Module 2

Module 1

Module 0

ECF

PCA Timer/Counter

ECCFn CCAPMn.0

CMOD.0

IEN0.6

IEN0.7

To Interrupt

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