Datasheet

43
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).
CF CR
CCON
0xD8
CH CL
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 ECCFnCAPPn
Cex.n
Capture