at89c5131 ATMEL Corporation, at89c5131 Datasheet - Page 55

• Manufacturer Part Number: at89c5131
• Description: 8-bit Flash Microcontroller With Full Speed Usb Device At89c5131
• Manufacturer: ATMEL Corporation

Programmable
Counter Array (PCA)
54
AT89C5131
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 64).
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 the port pin 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 five modules (see Figure 25). The timer
count source is determined from the CPS1 and CPS0 bits in the CMOD register
(Table 49) and can be programmed to run at:
•
•
•
•
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
Peripheral clock frequency (F
Peripheral clock frequency (F
Timer 0 overflow
External input on ECI (P1.2)
rising and/or falling edge capture,
software timer
high-speed output, or
pulse width modulator
1/6 the
1/2 the
The Timer 0 overflow
The input on the ECI pin (P1.2)
peripheral clock frequency (F
peripheral clock frequency (F
CLK PERIPH
CLK PERIPH
External I/O Pin
P1.2/ECI
P1.3/CEX0
P1.4/CEX1
P1.5/CEX2
P1.6/CEX3
P1.7/CEX4
)
)
CLK PERIPH
CLK PERIPH
÷
÷
2
6
)
)
.
.
4136C–USB–04/05