AT89LP51 Atmel Corporation, AT89LP51 Datasheet - Page 37

• Manufacturer Part Number: AT89LP51
• Manufacturer: Atmel Corporation

Specifications of AT89LP51

• Flash (kbytes): 4 Kbytes
• Max. Operating Frequency: 20 MHz
• Cpu: 8051-1C
• Max I/o Pins: 36
• Uart: 1
• Sram (kbytes): 0.25
• Eeprom (bytes): 256
• Self Program Memory: IAP
• Operating Voltage (vcc): 2.4 to 5.5
• Timers: 3
• Isp: SPI
• Watchdog: Yes

8.3
9. Interrupts
3709D–MICRO–12/11
Reducing Power Consumption
Figure 8-3.
Several possibilities need consideration when trying to reduce the power consumption in an
8051-based system. Generally, Idle or Power-down mode should be used as often as possible.
All unneeded functions should be disabled. The System Clock Divider can scale down the oper-
ating frequency during periods of low demand. The ALE output can be disabled by setting
DISALE in AUXR, thereby also reducing EMI.
The AT89LP51/52 provides 6 interrupt sources: two external interrupts, three timer interrupts,
and a serial port interrupt. These interrupts and the system reset each have a separate program
vector at the start of the program memory space. Each interrupt source can be individually
enabled or disabled by setting or clearing a bit in the interrupt enable register IE. The IE register
also contains a global disable bit, EA, which disables all interrupts.
Each interrupt source can be individually programmed to one of four priority levels by setting or
clearing bits in the interrupt priority registers IP and IPH. IP holds the low order priority bits and
IPH holds the high priority bits for each interrupt. An interrupt service routine in progress can be
interrupted by a higher priority interrupt, but not by another interrupt of the same or lower priority.
The highest priority interrupt cannot be interrupted by any other interrupt source. If two requests
of different priority levels are pending at the end of an instruction, the request of higher priority
level is serviced. If requests of the same priority level are pending at the end of an instruction, an
internal polling sequence determines which request is serviced. The polling sequence is based
on the vector address; an interrupt with a lower vector address has higher priority than an inter-
rupt with a higher vector address. Note that the polling sequence is only used to resolve pending
requests of the same priority level.
The External Interrupts INT0 and INT1 can each be either level-activated or edge-activated,
depending on bits IT0 and IT1 in Register TCON. The flags that actually generate these inter-
rupts are the IE0 and IE1 bits in TCON. When the service routine is vectored to, hardware clears
the flag that generated an external interrupt only if the interrupt was edge-activated. If the inter-
rupt was level activated, then the external requesting source (rather than the on-chip hardware)
controls the request flag.
The Timer 0 and Timer 1 Interrupts are generated by TF0 and TF1, which are set by a rollover in
their respective Timer/Counter registers (except for Timer 0 in Mode 3). When a timer interrupt is
generated, the on-chip hardware clears the flag that generated it when the service routine is
Internal
Internal
XTAL1
Reset
Clock
PWD
RST
Reset Recovery from Power-down (POL = 1)
t SUT
AT89LP51/52
37