PIC10F200/202/204/206
9.6.1
WDT PERIOD
9.5
Device Reset Timer (DRT)
The WDT has a nominal time-out period of 18 ms, (with
no prescaler). If a longer time-out period is desired, a
prescaler with a division ratio of up to 1:128 can be
assigned to the WDT (under software control) by
writing to the OPTION register. Thus, a time-out period
of a nominal 2.3 seconds can be realized. These peri-
ods vary with temperature, VDD and part-to-part
process variations (see DC specs).
On the PIC10F200/202/204/206 devices, the DRT runs
any time the device is powered up.
The DRT operates on an internal oscillator. The
processor is kept in Reset as long as the DRT is active.
The DRT delay allows VDD to rise above VDD min. and
for the oscillator to stabilize.
The on-chip DRT keeps the devices in a Reset
condition for approximately 18 ms after MCLR has
reached a logic high (VIH MCLR) level. Programming
GP3/MCLR/VPP as MCLR and using an external RC
network connected to the MCLR input is not required in
most cases. This allows savings in cost-sensitive and/
or space restricted applications, as well as allowing the
use of the GP3/MCLR/VPP pin as a general purpose
input.
Under worst-case conditions (VDD = Min., Temperature
= Max., max. WDT prescaler), it may take several
seconds before a WDT time-out occurs.
9.6.2
WDT PROGRAMMING
CONSIDERATIONS
The CLRWDT instruction clears the WDT and the
postscaler, if assigned to the WDT, and prevents it from
timing out and generating a device Reset.
The Device Reset Time delays will vary from chip-to-
chip due to VDD, temperature and process variation.
See AC parameters for details.
The SLEEP instruction resets the WDT and the
postscaler, if assigned to the WDT. This gives the
maximum Sleep time before a WDT wake-up Reset.
Reset sources are POR, MCLR, WDT time-out and
wake-up on pin change. See Section 9.9.2 “Wake-up
from Sleep”, Notes 1, 2 and 3.
TABLE 9-3:
DRT (DEVICE RESET TIMER
PERIOD)
Subsequent
POR Reset
Oscillator
Resets
INTOSC
18 ms (typical) 10 μs (typical)
9.6
Watchdog Timer (WDT)
The Watchdog Timer (WDT) is a free running on-chip
RC oscillator, which does not require any external
components. This RC oscillator is separate from the
internal 4 MHz oscillator. This means that the WDT will
run even if the main processor clock has been stopped,
for example, by execution of a SLEEP instruction.
During normal operation or Sleep, a WDT Reset or
wake-up Reset, generates a device Reset.
The TO bit (STATUS<4>) will be cleared upon a
Watchdog Timer Reset.
The WDT can be permanently disabled by program-
ming the configuration WDTE as a ‘0’ (see Section 9.1
“Configuration Bits”). Refer to the PIC10F200/202/
204/206 Programming Specifications to determine how
to access the Configuration Word.
DS41239D-page 46
© 2007 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
