AT89C51ID2-SLSIM Atmel, AT89C51ID2-SLSIM Datasheet - Page 40

• Manufacturer Part Number: AT89C51ID2-SLSIM
• Description: C51ID2 64KF TWI 32KHZ PLCC44 3-5.5V IND.
• Manufacturer: Atmel

Programmable
Counter Array PCA
4289C–8051–11/05
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 51).
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 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 14). The timer
count source is determined from the CPS1 and CPS0 bits in the CMOD register
(Table 27) and can be programmed to run at:
•
•
•
•
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
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
PCA component
16-bit Module 0
16-bit Module 1
16-bit Module 2
16-bit Module 3
16-bit Counter
CLK PERIPH
CLK PERIPH
)
)
CLK PERIPH
CLK PERIPH
÷
÷
2
6
)
)
External I/O Pin
P1.3 / CEX0
P1.4 / CEX1
P1.5 / CEX2
P1.6 / CEX3
P1.2 / ECI
AT89C51ID2
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