AT89C51ED2 Atmel Corporation, AT89C51ED2 Datasheet - Page 46

• Manufacturer Part Number: AT89C51ED2
• Manufacturer: Atmel Corporation

Specifications of AT89C51ED2

• Flash (kbytes): 64 Kbytes
• Max. Operating Frequency: 60 MHz
• Cpu: 8051-12C
• Max I/o Pins: 32
• Spi: 1
• Uart: 1
• Sram (kbytes): 2
• Eeprom (bytes): 2048
• Self Program Memory: API
• Operating Voltage (vcc): 2.7 to 5.5
• Timers: 4
• Isp: UART
• Watchdog: Yes

13.5
46
PCA Watchdog Timer
AT89C51RD2/ED2
Figure 13-6. PCA PWM Mode
An on-board watchdog timer is available with the PCA to improve the reliability of the system
without increasing chip count. Watchdog timers are useful for systems that are susceptible to
noise, power glitches, or electrostatic discharge. Module 4 is the only PCA module that can be
programmed as a watchdog. However, this module can still be used for other modes if the
watchdog is not needed. Figure 13-4 shows a diagram of how the watchdog works. The user
pre-loads a 16-bit value in the compare registers. Just like the other compare modes, this 16-bit
value is compared to the PCA timer value. If a match is allowed to occur, an internal reset will be
generated. This will not cause the RST pin to be driven high.
In order to hold off the reset, the user has three options:
1. Periodically change the compare value so it will never match the PCA timer.
2. Periodically change the PCA timer value so it will never match the compare values.
3. Disable the watchdog by clearing the WDTE bit before a match occurs and then re-
enable it.
ECOMn
CAPPn
Enable
CAPNn MATn TOGn PWMn ECCFn
Overflow
PCA Counter/Timer
8-bit Comparator
CCAPnH
CCAPnL
CL
CCAPMn, n= 0 to 4
0xDA to 0xDE
“1”
“0”
4235K–8051–05/08
CEXn