DS87C530 Maxim, DS87C530 Datasheet - Page 27

• Manufacturer Part Number: DS87C530
• Description: The DS87C530/DS83C530 EPROM/ROM microcontrollers with a real-time clock (RTC) are 8051-compatible microcontrollers based on the Dallas Semiconductor high-speed core
• Manufacturer: Maxim

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
SCON0
SCON1
NAME
WDTI
RTCI
INT2
INT4
INT0
INT1
INT3
INT5
TF0
TF1
TF2
PFI
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
FUNCTION
DS87C530/DS83C530 EPROM/ROM Microcontrollers with Real-Time Clock
27 of 45
VECTOR
0Bh
1Bh
2Bh
3Bh
4Bh
5Bh
6Bh
33h
03h
13h
23h
43h
53h
63h
PRIORITY
NATURAL
10
11
12
13
14
1
2
3
4
5
6
7
8
9
8051/DALLAS
DALLAS
DALLAS
DALLAS
DALLAS
DALLAS
DALLAS
DALLAS
DALLAS
8051
8051
8051
8051
8051
8051