AT89C51ED2-RDTUM datasheet(43/137 Pages) ATMEL

43 / 137 page

4235K–8051–05/08

AT89C51RD2/ED2

13.1

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

CCAPnH). 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 13-3).

Figure 13-3. PCA Capture Mode

13.2

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 13-4).

CCON

0xD8

CCAPnH

CCAPnL

CCF4 CCF3 CCF2

CCF1 CCF0

PCA IT

PCA Counter/Timer

ECOMn

CCAPMn, n= 0 to 4

0xDA to 0xDE

CAPNn MATn TOGn PWMn ECCFn

CAPPn

Cex.n

Capture

AT89C51ED2-RDTUM 数据表(PDF) 43 Page - ATMEL Corporation