AT89C55WD Atmel Corporation, AT89C55WD Datasheet - Page 16

• Manufacturer Part Number: AT89C55WD
• Manufacturer: Atmel Corporation

Specifications of AT89C55WD

• Flash (kbytes): 20 Kbytes
• Max. Operating Frequency: 24 MHz
• Cpu: 8051-12C
• Max I/o Pins: 32
• Uart: 1
• Sram (kbytes): 0.25
• Operating Voltage (vcc): 4.0 to 6.0
• Timers: 3
• Watchdog: Yes

Figure 14-1. Timer 2 in Clock-Out Mode
15. Interrupts
16
(T2EX)
P1.0
P1.1
(T2)
AT89C55WD
OSC
TRANSITION
DETECTOR
The AT89C55WD has a total of six interrupt vectors: two external interrupts (INT0 and INT1),
three timer interrupts (Timers 0, 1, and 2), and the serial port interrupt. These interrupts are all
shown in
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 Table 5 shows that bit position IE.6 is unimplemented. User software should not write
a ‘1’ to this bit position, since it may be used in future AT89 products.
Timer 2 interrupt is generated by the logical OR of bits TF2 and EXF2 in register T2CON. Nei-
ther of these flags is cleared by hardware when the service routine is vectored to. In fact, the
service routine may have to determine whether it was TF2 or EXF2 that generated the interrupt,
and that bit will have to be cleared in software.
÷2
Figure
15-1.
EXEN2
C/T2 BIT
EXF2
TR2
÷2
TIMER 2
INTERRUPT
(8-BITS)
RCAP2L RCAP2H
TL2
T2OE (T2MOD.1)
(8-BITS)
TH2
1921D–MICRO–6/08