AT89S51 Atmel Corporation, AT89S51 Datasheet - Page 11

• Manufacturer Part Number: AT89S51
• Manufacturer: Atmel Corporation

Specifications of AT89S51

• Flash (kbytes): 4 Kbytes
• Max. Operating Frequency: 24 MHz
• Cpu: 8051-12C
• Max I/o Pins: 32
• Uart: 1
• Sram (kbytes): 0.125
• Operating Voltage (vcc): 4.0 to 5.5
• Timers: 2
• Isp: SPI
• Watchdog: Yes

10. Interrupts
2487D–MICRO–6/08
The AT89S51 has a total of five interrupt vectors: two external interrupts (INT0 and INT1), two
timer interrupts (Timers 0 and 1), and the serial port interrupt. These interrupts are all shown in
Figure
Each of these interrupt sources can be individually enabled or disabled by setting or clearing a
bit in Special Function Register IE. IE also contains a global disable bit, EA, which disables all
interrupts at once.
Note that
should not write 1s to these bit positions, since they may be used in future AT89 products.
The Timer 0 and Timer 1 flags, TF0 and TF1, are set at S5P2 of the cycle in which the timers
overflow. The values are then polled by the circuitry in the next cycle.
Table 10-1.
Symbol
EA
–
–
ES
ET1
EX1
ET0
EX0
User software should never write 1s to reserved bits, because they may be used in future AT89
products.
(MSB)
Enable Bit = 1 enables the interrupt.
Enable Bit = 0 disables the interrupt.
10-1.
EA
Table 10-1
Interrupt Enable (IE) Register
–
shows that bit positions IE.6 and IE.5 are unimplemented. User software
Position
IE.7
IE.6
IE.5
IE.4
IE.3
IE.2
IE.1
IE.0
–
ES
Function
Serial Port interrupt enable bit
External interrupt 1 enable bit
External interrupt 0 enable bit
Disables all interrupts. If EA = 0, no interrupt is
acknowledged. If EA = 1, each interrupt source is
individually enabled or disabled by setting or clearing its
enable bit.
Reserved
Reserved
Timer 1 interrupt enable bit
Timer 0 interrupt enable bit
ET1
(LSB)
EX1
ET0
AT89S51
EX0
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