Datasheet

PIC18F87J50 FAMILY
DS39775C-page 358 © 2009 Microchip Technology Inc.
25.2 Watchdog Timer (WDT)
For PIC18F87J10 family devices, the WDT is driven by
the INTRC oscillator. When the WDT is enabled, the
clock source is also enabled. The nominal WDT period is
4 ms and has the same stability as the INTRC oscillator.
The 4 ms period of the WDT is multiplied by a 16-bit
postscaler. Any output of the WDT postscaler is selected
by a multiplexor, controlled by the WDTPS bits in Config-
uration Register 2H. Available periods range from about
4 ms to 135 seconds (2.25 minutes depending on
voltage, temperature and WDT postscaler). The WDT
and postscaler are cleared whenever a SLEEP or
CLRWDT instruction is executed, or a clock failure
(primary or Timer1 oscillator) has occurred.
25.2.1 CONTROL REGISTER
The WDTCON register (Register 25-9) is a readable
and writable register. The SWDTEN bit enables or dis-
ables WDT operation. This allows software to override
the WDTEN Configuration bit and enable the WDT only
if it has been disabled by the Configuration bit.
The ADSHR bit selects which SFRs currently are
selected and accessible. For additional details, see
Section 5.3.5.1 “Shared Address SFRs”.
LVDSTAT is a read-only status bit that is continuously
updated and provides information about the current
level of V
DDCORE. This bit is only valid when the on-chip
voltage regulator is enabled.
FIGURE 25-1: WDT BLOCK DIAGRAM
Note 1: The CLRWDT and SLEEP instructions
clear the WDT and postscaler counts
when executed.
2: When a CLRWDT instruction is executed,
the postscaler count will be cleared.
INTRC Oscillator
WDT
Wake-up from
Reset
WDT
WDT Counter
Programmable Postscaler
1:1 to 1:32,768
Enable WDT
WDTPS3:WDTPS0
SWDTEN
CLRWDT
4
Power-Managed
Reset
All Device Resets
Sleep
INTRC Control
÷128
Modes