AT89LP51RB2 datasheet(101/254 Pages) ATMEL

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101

3722A–MICRO–10/11

AT89LP51RB2/RC2/IC2 Preliminary

15.3

PCA Capture Mode

To use one of the PCA modules in the capture mode either one or both of the CCAPM bits

CAPN and CAPP for that module must be set. The external CEX input for the module (on port 1)

is sampled for a transition. When a valid transition occurs the PCA hardware loads the value of

the PCA counter registers (CH and CL) into the module's capture registers (CCAPnL and CCA-

PnH). If the CCFn bit for the module in the CCON SFR and the ECCFn bit in the CCAPMn SFR

are set then an interrupt will be generated (Refer to Figure 15-3).

Figure 15-3. PCA Capture Mode

15.4

16-bit Software Timer/ Compare Mode

The PCA modules can be used as software timers by setting both the ECOM and MAT bits in

the modules CCAPMn register. The PCA timer will be compared to the module's capture regis-

ters and when a match occurs an interrupt will occur if the CCFn (CCON SFR) and the ECCFn

(CCAPMn SFR) bits for the module are both set (See Figure 15-4).

Figure 15-4. PCA Compare Mode and PCA Watchdog Timer

Before enabling ECOM bit, CCAPnL and CCAPnH should be set with a non zero value, other-

wise an unwanted match could happen. Writing to CCAPnH will set the ECOM bit. Once ECOM

is set, writing CCAPnL will clear ECOM so that an unwanted match doesn’t occur while modify-

ing the compare value. Writing to CCAPnH will set ECOM. For this reason, user software should

write CCAPnL first, and then CCAPnH. Of course, the ECOM bit can still be controlled by

accessing to CCAPMn register.

CCAPnL

CCAPnH

Interrupt

CEXn

CCFn

CCAPMn.0

ECCFn

CAPNn

CCAPMn.4

CAPPn

CCAPMn.5

Module n

CCAPnL

CCAPnH

Interrupt

CCFn

MATn

CCAPMn.3

ECOMn

Write to

CCAPnH

Write to

CCAPnL

ECCFn

CCAPMn.0

WDTE

CMOD.6 (Module 4 only)

Module n

Reset

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