DS87C530_05 Datasheet, PDF (27/47 Pages) Dallas Semiconductor – EPROM/ROM Microcontrollers with Real-Time Clock

DS87C530/DS83C530 EPROM/ROM Microcontrollers with Real-Time Clock
There are five control bits in special function registers that affect the Watchdog Timer and two status
flags that report to the user. WDIF (WDCON.3) is the interrupt flag that is set at timer termination when
there are 512 clocks remaining until the reset flag is set. WTRF (WDCON.2) is the flag that is set when
the timer has completely timed out. This flag is normally associated with a CPU reset and allows software
to determine the reset source. EWT (WDCON.1) is the enable for the Watchdog Timer reset function.
RWT (WDCON.0) is the bit that software uses to restart the Watchdog Timer. Setting this bit restarts the
timer for another full interval. Application software must set this bit before the timeout. Both of these bits
are protected by Timed Access discussed below. As mentioned previously, WD1 and 0 (CKCON .7 and
6) select the timeout. The Reset Watchdog Timer bit (WDCON.0) should be asserted prior to modifying
the Watchdog Timer Mode Select bits (WD1, WD0) to avoid corruption of the watchdog count. Finally,
the user can enable the Watchdog Interrupt using EWDI (EIE.4).
INTERRUPTS
The DS87C530/DS83C530 provide 14 interrupt sources with three priority levels. The Power-Fail
Interrupt (PFI) has the highest priority. Software can assign high or low priority to other sources. All
interrupts that are new to the 8051 family, except for the PFI, have a lower natural priority than the
originals.
Table 8. Interrupt Sources and Priorities
NAME
FUNCTION
PFI
INT0
TF0
INT1
TF1
SCON0
TF2
SCON1
INT2
INT3
INT4
INT5
WDTI
RTCI
Power-Fail Interrupt
External Interrupt 0
Timer 0
External Interrupt 1
Timer 1
TI0 or RI0 from Serial Port 0
Timer 2
TI1 or RI1 from Serial Port 1
External Interrupt 2
External Interrupt 3
External Interrupt 4
External Interrupt 5
Watchdog Timeout Interrupt
RTC Interrupt
VECTOR
33h
03h
0Bh
13h
1Bh
23h
2Bh
3Bh
43h
4Bh
53h
5Bh
63h
6Bh
NATURAL
PRIORITY
1
2
3
4
5
6
7
8
9
10
11
12
13
14
8051/DALLAS
DALLAS
8051
8051
8051
8051
8051
8051
DALLAS
DALLAS
DALLAS
DALLAS
DALLAS
DALLAS
DALLAS
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