080505
OPERATIONS MANUAL PPM-GX500
13
Watchdog Timer
The PPM-GX500 features a watchdog timer, which can be used to guard against
software lockups. When a jumper is placed on pins 3-4 of
J1
, the watchdog circuit is
totally disabled and can never reset the processor. When pins 3 and 4 are left open,
the circuit will function as configured from the CMOS setup utility. (See description in
BIOS Supplemental
.) The selection in the CMOS setting serves as the default timeout
value as the processor boots, but can be changed in the application software as shown
below. The BIOS option is for enabling the watchdog only during boot. When the
watchdog is disabled at boot, it can be re-enabled through application software. The
watchdog timer is serviced by writing any value to I/O port 1EFH. If the watchdog is
not serviced within the allotted time, the circuit resets the CPU.
Note:
It is recommended that the long timeout (300 seconds) be used with the
watchdog enabled when trying to boot any operating system.
Speaker
An on-board speaker is available for sound generation. A beep code is generated
that corresponds to any BIOS error codes (if required) during the power-up or reset
sequence.
Visual
Index
Status LED
A red status LED is populated on the board at
D5
which can be used for any application
specific purpose. The LED can be turned on in software by writing a
1
to I/O port
1EDH. The LED can be turned off by writing a
0
to 1EDH. The signal is also available
on
J8
as LED 3.
Visual
Index
2 4
o o
o o
1 3
Enabled
(default)
J1
2 4
o o
o o
1 3
Disabled
Watchdog Timer (must be enabled at J1)
Port Address
Value
Reset Interval
1EEH
00h
DISABLED
01h
3 SECONDS
03h
30 SECONDS
05h
300 SECONDS
1EFH
ANY
RESET TIMER
