Specifications

Little Board/P5i Technical Manual
2–44
Table 2–35 J8 Mating Connector
Connector
Type Mating Connector
RIBBON 3M 3473-7600
DISCRETE WIRE MOLEX HOUSING 22-55-2102
Pin 16-02-0103
2.13 BATTERY-BACKED CLOCK
An AT-compatible battery-backed real-time clock (with CMOS RAM) is standard on the Little
Board/P5i. The clock is powered by a 3.0 volt Lithium battery soldered to the board. Battery drain for
the clock is less than 0.4 uA. This battery will support the clock for about 10 years.
The factory initializes the real-time clock and various parameters in the configuration memory for a
standard configuration. The factory sets the date and time, but it may not be set for your time zone. Use
SETUP to change these values as needed.
The contents of the configuration memory are also stored in an onboard EEPROM. The ROM BIOS
reads the EEPROM to get configuration information if the CMOS RAM data is lost. This means that the
board will function if the battery fails. Note that without a battery, the real-time clock date and time will
not be correct.
2.14 WATCHDOG TIMER
A unique feature of the on-board clock circuitry is a watchdog timer. You can program this timer to
generate an interrupt or reset signal if the programmed time interval expires before the timer is
reinitialized. Use SETUP to select the time interval. The options are: Disable, 30 seconds, 60 seconds,
and 90 seconds.
The watchdog timer uses the standard alarm feature of the real-time clock. In a standard AT, the alarm
output is connected to IRQ8. On the Little Board/P5i you can also jumper W24 to connect the alarm
output to I/O Channel Check (-IOCHCK) or Reset. I/O Channel Check is the bus signal that triggers a
non-maskable interrupt (NMI). Reset is a hard reset signal, the same as pressing the Reset button. Jumper
W24 as shown in Figure 2–11. To disable the watchdog timer, leave W24 open, and select Watchdog
Timer Disable in SETUP.
If you enable the watchdog timer in SETUP, but do not install a jumper on W24, IRQ8 will turn off the
interrupt and the system will continue, unaffected. If you select I/O Channel Check, the watchdog timer
will generate a message on the screen. Install your own interrupt handler to cause the watchdog timer to
trigger a different response. If you select Reset, no interrupt handler is required.
Figure 2–11 Watchdog Timer Response Jumper (W24)