PIC18F2220 MICROCHIP [Microchip Technology], PIC18F2220 Datasheet - Page 247

• Manufacturer Part Number: PIC18F2220
• Description: 28/40/44-Pin High-Performance, Enhanced Flash Microcontrollers with 10-Bit A/D and nanoWatt Technology
• Manufacturer: MICROCHIP [Microchip Technology]

23.2
For PIC18F2X20/4X20 devices, the WDT is driven by
the INTRC source. 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 multiplexer, controlled by bits in Configu-
ration Register 2H. Available periods range from 4 ms
to 131.072 seconds (2.18 minutes). The WDT and
postscaler are cleared when any of the following events
occur: execute a SLEEP or CLRWDT instruction, the
IRCF bits (OSCCON<6:4>) are changed or a clock
failure has occurred.
Adjustments to the internal oscillator clock period using
the OSCTUNE register also affect the period of the
WDT by the same factor. For example, if the INTRC
period is increased by 3%, then the WDT period is
increased by 3%.
FIGURE 23-1:
 2003 Microchip Technology Inc.
Change on IRCF bits
All Device Resets
Watchdog Timer (WDT)
INTRC Source
WDTPS<3:0>
SWDTEN
CLRWDT
WDTEN
Sleep
WDT BLOCK DIAGRAM
Enable WDT
WDT Counter
PIC18F2220/2320/4220/4320
125
INTRC Control
4
Programmable Postscaler
1:1 to 1:32,768
23.2.1
Register 23-14 shows the WDTCON register. This is a
readable and writable register which contains a control
bit that allows software to override the WDT enable
configuration bit, but only if the configuration bit has
disabled the WDT.
Note 1: The CLRWDT and SLEEP instructions
2: Changing the setting of the IRCF bits
3: When a CLRWDT instruction is executed,
CONTROL REGISTER
clear the WDT and postscaler counts
when executed.
(OSCCON<6:4> clears the WDT and
postscaler counts.
the postscaler count will be cleared.
WDT
Reset
DS39599C-page 245
Wake-up
from Sleep
WDT
Reset