Rainbow Electronics T89C51CC02 - Manual (Page 102)

102 Rev.A - May 17, 2001
Preliminary
T89C51CC02
16. Programmable Counter Array PCA
16.1. Introduction
The PCA provides more timing capabilities with less CPU intervention than the standard timer/counters. Its
advantages include reduced software overhead and improved accuracy. The PCA consists of a dedicated timer/
counter which serves as the time base for an array of two compare/capture modules. Its clock input can be
programmed to count any of the following signals:
•
PCA clock frequency / 6
•
PCA clock frequency / 2
•
Timer 0 overflow
•
External input on ECI (P1.2)
Each compare/capture modules can be programmed in any one of the following modes:
•
rising and/or trailing edge capture,
•
software timer,
•
high-speed output,
•
pulse width modulator.
When the compare/capture modules are programmed in capture mode, software timer, or high speed output mode,
an interrupt can be generated when the module executes its function. All two modules plus the PCA timer overflow
share one interrupt vector.
The PCA timer/counter and compare/capture modules share Port 1 for external I/Os. These pins are listed below.
If the port is not used for the PCA, it can still be used for standard I/O.
The PCA timer is a common time base for all modules (see Figure 9). The timer count source is determined from
the CPS1 and CPS0 bits in the CMOD SFR (see Table 8) and can be programmed to run at:
•
1/6 the PCA clock frequency.
•
1/2 the PCA clock frequency.
•
the Timer 0 overflow.
•
the input on the ECI pin (P1.2).
PCA component External I/O Pin
16-bit Counter P1.2 / ECI
16-bit Module 0 P1.3 / CEX0
16-bit Module 1 P1.4 / CEX1