AT89C51RD2 Atmel Corporation, AT89C51RD2 Datasheet - Page 26

• Manufacturer Part Number: AT89C51RD2
• Manufacturer: Atmel Corporation

Specifications of AT89C51RD2

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

10. Reset
10.1
10.2
10.3
26
Introduction
Reset Input
Reset Output
AT89C51RD2/ED2
The reset sources are: Power Management, Hardware Watchdog, PCA Watchdog and Reset
input.
Figure 10-1. Reset schematic
The Reset input can be used to force a reset pulse longer than the internal reset controlled by
the Power Monitor. RST input has a pull-down resistor allowing power-on reset by simply con-
necting an external capacitor to V
characteristics are discussed in the Section “DC Characteristics” of the AT89C51RD2/ED2
datasheet.
Figure 10-2. Reset Circuitry and Power-On Reset
Reset output can be generated by two sources:
As detailed in Section “Hardware Watchdog Timer”, page 84, the WDT generates a 96-clock
period pulse on the RST pin.
In order to properly propagate this pulse to the rest of the application in case of external capaci-
tor or power-supply supervisor circuit, a 1 kΩ resistor must be added as shown Figure 10-3.
• Internal POR/PFD
• Hardware watchdog timer
RST
RST
Watchdog
Watchdog
Hardware
a. RST input circuitry
Monitor
VSS
Power
PCA
CC
as shown in Figure 10-2. Resistor value and input
To internal reset
b. Power-on Reset
Internal Reset
VDD
+
RST
4235K–8051–05/08