PIC16F882-I Datasheet, PDF (226/328 Pages) Microchip Technology – 28/40/44-Pin, Enhanced Flash-Based 8-Bit CMOS Microcontrollers

PIC16F882/883/884/886/887
14.5 Watchdog Timer (WDT)
The WDT has the following features:
• Operates from the LFINTOSC (31 kHz)
• Contains a 16-bit prescaler
• Shares an 8-bit prescaler with Timer0
• Time-out period is from 1 ms to 268 seconds
• Configuration bit and software controlled
WDT is cleared under certain conditions described in
Table 14-7.
14.5.1 WDT OSCILLATOR
The WDT derives its time base from the 31 kHz
LFINTOSC. The LTS bit of the OSCCON register does
not reflect that the LFINTOSC is enabled.
The value of WDTCON is ‘---0 1000’ on all Resets.
This gives a nominal time base of 17 ms.
Note:
When the Oscillator Start-up Timer (OST)
is invoked, the WDT is held in Reset,
because the WDT Ripple Counter is used
by the OST to perform the oscillator delay
count. When the OST count has expired,
the WDT will begin counting (if enabled).
14.5.2 WDT CONTROL
The WDTE bit is located in the Configuration Word
Register 1. When set, the WDT runs continuously.
When the WDTE bit in the Configuration Word
Register 1 is set, the SWDTEN bit of the WDTCON
register has no effect. If WDTE is clear, then the
SWDTEN bit can be used to enable and disable the
WDT. Setting the bit will enable it and clearing the bit
will disable it.
The PSA and PS<2:0> bits of the OPTION register
have the same function as in previous versions of the
PIC16F882/883/884/886/887 Family of microcon-
trollers. See Section 5.0 “Timer0 Module” for more
information.
FIGURE 14-9:
WATCHDOG TIMER BLOCK DIAGRAM
From TMR0 Clock Source
0
16-bit WDT Prescaler
1
Prescaler⁽¹⁾
8
31 kHz
LFINTOSC Clock
WDTPS<3:0>
WDTE from the Configuration Word Register 1
SWDTEN from WDTCON
PSA
PS<2:0>
0
1
PSA
WDT Time-out
Note 1: This is the shared Timer0/WDT prescaler. See Section 5.1.3 “Software Programmable Prescaler” for more information.
TABLE 14-7: WDT STATUS
Conditions
WDTE = 0
CLRWDT Command
Oscillator Fail Detected
Exit Sleep + System Clock = T1OSC, EXTRC, INTOSC, EXTCLK
Exit Sleep + System Clock = XT, HS, LP
WDT
Cleared
Cleared until the end of OST
DS41291F-page 224
© 2009 Microchip Technology Inc.