PIC18F87J10 Datasheet, PDF (275/394 Pages) Microchip Technology – 64/80-Pin High-Performance, 1-Mbit Flash Microcontrollers with nanoWatt Technology

PIC18F87J10 FAMILY
23.2 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 Configuration Register 2H. Available periods range
from 4 ms to 131.072 seconds (2.18 minutes). The
WDT and postscaler are cleared whenever a SLEEP or
CLRWDT instruction is executed, or a clock failure
(primary or Timer1 oscillator) has occurred.
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.
23.2.1 CONTROL REGISTER
The WDTCON register (Register 23-9) 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.
FIGURE 23-1:
WDT BLOCK DIAGRAM
SWDTEN
INTRC Oscillator
Enable WDT
INTRC Control
WDT Counter
÷128
CLRWDT
All Device Resets
WDTPS3:WDTPD0
Sleep
Programmable Postscaler ^Reset
1:1 to 1:32,768
WDT
4
Wake-up from
Power-Managed
Modes
WDT
Reset
REGISTER 23-9:
WDTCON: WATCHDOG TIMER CONTROL REGISTER
U-0
U-0
U-0
U-0
U-0
U-0
—
—
—
—
—
—
bit 7
U-0
R/W-0
—
SWDTEN⁽¹⁾
bit 0
bit 7-1
bit 0
Unimplemented: Read as ‘0’
SWDTEN: Software Controlled Watchdog Timer Enable bit⁽¹⁾
1 = Watchdog Timer is on
0 = Watchdog Timer is off
Note 1: This bit has no effect if the configuration bit, WDTEN, is enabled.
Legend:
R = Readable bit
-n = Value at POR
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared x = Bit is unknown
TABLE 23-2: SUMMARY OF WATCHDOG TIMER REGISTERS
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Reset Values
on page
RCON
IPEN
—
—
RI
TO
PD
POR
BOR
50
WDTCON
—
—
—
—
—
—
— SWDTEN
50
Legend: — = unimplemented, read as ‘0’. Shaded cells are not used by the Watchdog Timer.
 2005 Microchip Technology Inc.
Advance Information
DS39663A-page 273