PCA is Programmable Counter Area.
It was first time in INTEL 83C51FA/FB/FC.
The PCA consist of dedicated 16 bit timer/counter which seves as the time base for an array of five compare/capture modules (16 bit).
Each of five modules can be programmed in capture, software timer, high speed output, wd timer, or pwm mode.
see INTEL or PHILIPS web site for more info...