DS87C520 datasheet(24/45 Pages) DALLAS

24 / 45 page

DS87C520/DS83C520 EPROM/ROM High-Speed Microcontrollers

24 of 45

will set an interrupt flag. Regardless of whether the user enables this interrupt, there are then 512 clocks

left until the reset flag is set. Software can enable the interrupt and reset individually. Note that the

Watchdog is a free running timer and does not require an enable.

There are 5 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. 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). The Special Function Register map is shown above.

INTERRUPTS

The DS87C520/DS83C520 provide 13 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

PRIORITY

8051/DALLAS

PFI

Power-Fail Interrupt

33h

DALLAS

INT0

External Interrupt 0

03h

8051

TF0

Timer 0

0Bh

8051

INT1

External Interrupt 1

13h

8051

TF1

Timer 1

1Bh

8051

SCON0

TI0 or RI0 from serial port 0

23h

8051

TF2

Timer 2

2Bh

8051

SCON1

TI1 or RI1 from serial port 1

3Bh

DALLAS

INT2

External Interrupt 2

43h

DALLAS

INT3

External Interrupt 3

4Bh

DALLAS

INT4

External Interrupt 4

53h

DALLAS

INT5

External Interrupt 5

5Bh

DALLAS

WDTI

Watchdog Timeout Interrupt

63h

DALLAS

DS87C520 Datasheet(PDF) 24 Page - Dallas Semiconductor

DS87C520 Datasheet(HTML) 24 Page - Dallas Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

Datasheet Download

Link URL