
39
AT89C51RB2/RC2
4180E–8051–10/06
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 Mod-
ule (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
Figure 13. PCA Capture Mode
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 ECCFn
CAPPn
Cex. n
Capture