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

VECTOR

NATURAL

8051/DALLAS

PRIORITY

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PFI

Power-Fail Interrupt

33h

1

DALLAS

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

External Interrupt 0

03h

2

8051

INT0

 

 

 

 

 

 

 

 

 

 

 

TF0

Timer 0

0Bh

3

8051

 

 

 

 

 

 

 

 

 

 

 

 

 

 

External Interrupt 1

13h

4

8051

INT1

 

 

 

 

 

 

 

 

 

 

TF1

Timer 1

1Bh

5

8051

 

 

 

 

 

 

 

SCON0

TI0 or RI0 from Serial Port 0

23h

6

8051

 

 

 

 

 

 

 

 

 

 

TF2

Timer 2

2Bh

7

8051

 

 

 

 

 

 

 

SCON1

TI1 or RI1 from Serial Port 1

3Bh

8

DALLAS

 

 

 

 

 

 

 

INT2

External Interrupt 2

43h

9

DALLAS

 

 

 

 

 

 

 

 

 

 

 

 

 

External Interrupt 3

4Bh

10

DALLAS

 

INT3

 

 

 

 

 

INT4

External Interrupt 4

53h

11

DALLAS

 

 

 

 

 

 

 

 

 

 

 

 

 

External Interrupt 5

5Bh

12

DALLAS

 

INT5

WDTI

Watchdog Timeout Interrupt

63h

13

DALLAS

 

 

 

 

 

RTCI

RTC Interrupt

6Bh

14

DALLAS

 

 

 

 

 

 

 

 

 

 

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