t89c51rd2-slscl ATMEL Corporation, t89c51rd2-slscl Datasheet - Page 23

• Manufacturer Part Number: t89c51rd2-slscl
• Description: 0 To 40 Mhz Flash Programmable 8-bit Microcontroller
• Manufacturer: ATMEL Corporation

Programmable Counter
Array PCA
4243G–8051–05/03
The PCA provides more timing capabilities with less CPU intervention than the standard
timer/counters. Its advantages include reduced software overhead and improved accu-
racy. The PCA consists of a dedicated timer/counter which serves as the time base for
an array of five compare/ capture modules. Its clock input can be programmed to count
any one of the following signals:
•
•
•
•
Each compare/capture modules can be programmed in any one of the following modes:
•
•
•
•
Module 4 can also be programmed as a watchdog timer (See Section "PCA Watchdog
Timer", page 32).
When the compare/capture modules are programmed in the capture mode, software
timer, or high speed output mode, an interrupt can be generated when the module exe-
cutes its function. All five modules plus the PCA timer overflow share one interrupt
vector.
The PCA timer/counter and compare/capture modules share Port 1 for external I/O.
These pins are listed below. If one or several bits in the port are not used for the PCA,
they can still be used for standard I/O.
The PCA timer is a common time base for all five modules (See Figure 7). The timer
count source is determined from the CPS1 and CPS0 bits in the CMOD SFR (See
Table 10) and can be programmed to run at:
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•
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PCA component
16-bit Counter
16-bit Module 0
16-bit Module 1
16-bit Module 2
16-bit Module 3
16-bit Module 4
Oscillator frequency
Oscillator frequency
Timer 0 overflow
External input on ECI (P1.2)
rising and/or falling edge capture,
software timer,
high-speed output, or
pulse width modulator.
1/12 the oscillator frequency. (Or 1/6 in X2 Mode)
1/4 the oscillator frequency. (Or 1/2 in X2 Mode)
The Timer 0 overflow
The input on the ECI pin (P1.2)
÷
÷
12 (
4 (
÷
÷
2 in X2 mode)
6 in X2 mode)
External I/O Pin
P1.2 / ECI
P1.3 / CEX0
P1.4 / CEX1
P1.5 / CEX2
P1.6 / CEX3
P1.7 / CEX4
T89C51RD2
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