DS80C320_06 Datasheet, PDF (16/40 Pages) Maxim Integrated Products – High-Speed/Low-Power Microcontrollers

DS80C320/DS80C323 High-Speed/Low-Power Microcontrollers
a 25MHz crystal frequency. Note that once the counter chain has reached a conclusion, the optional
interrupt is generated. Regardless of whether the user enables this interrupt, there are then 512 clocks left
until a reset occurs. There are 5 control bits in special function registers that affect the Watchdog Timer
and two status flags that report to the user. 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.
WDIF (WDCON.3) is the interrupt flag that is set when there are 512 clocks remaining until a reset
occurs. WTRF (WDCON.2) is the flag that is set when a Watchdog reset has occurred. This allows the
application software to determine the source of a reset.
Setting the EWT (WDCON.1) bit enables the Watchdog Timer. The bit is protected by timed access.
Setting the RWT (WDCON.0) bit restarts the Watchdog Timer for another full interval. Application
software must set this bit prior to the timeout. As mentioned previously, WD1 and 0 (CKCON .7 and 6)
select the timeout. Finally, the Watchdog Interrupt is enabled using EWDI (EIE.4).
INTERRUPTS
The DS80C320/DS80C323 provide 13 sources of interrupt with three priority levels. The Power-fail
Interrupt (PFI), if enabled, always has the highest priority. There are two remaining user-selectable
priorities: high and low. If two interrupts that have the same priority occur simultaneously, the natural
precedence given in Table 4 determines which is acted upon. Except for the PFI, all interrupts that are
new to the 8051 family have a lower natural priority than the originals.
Table 4. Interrupt Priority
NAME
FUNCTION
PFI
INT0
TF0
INT1
TF1
SCON0
TF2
SCON1
INT2
INT3
INT4
INT5
WDTI
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
VECTOR
33h j
03h
0Bh
13h
1Bh
23h
2Bh
3Bh
43h
4Bh
53h
5Bh
63h
NATURAL
PRIORITY
1
2
3
4
5
6
7
8
9
10
11
12
13
OLD/NEW
New
Old
Old
Old
Old
Old
Old
New
New
New
New
New
New
16 of 40