Acrosser AR-B1790 - Manual (Page 23)

AR-B1790 User’s Guide
23
4. WATCHDOG TIMER
This section describes the use of Watchdog Timer, including disable, enable, and trigger. AR-B1790 is equipped
with a programmable time-out period watchdog timer that occupies I/O port 443H. Users can use simple program to
enable the watchdog timer. Once you enable the watchdog timer, the program should trigger it every time before it
times out. Watchdog Timer will generate a response (system or IRQ9) due to system fails to trigger or disable
watchdog timer before preset timer, times out.
Watchdog
Register
Time Base
Counter and
Compartor
RESET
Enable(D7)
Time Factor
(D0-D5)
Write and
Trigger
Watchdog Block Diagram
4.1 WATCHDOG TIMER SETTING
The watchdog timer is a circuit that maybe be used from your program software to detect crash or hang up.
The Watchdog timer is automatically disabled after reset. Once you enabled the watchdog timer, your program
should trigger the watchdog timer every time before it times out. After you trigger the watchdog timer, the timer will
be set to zero and start to count again. If your program fails to trigger the watchdog timer before times out, it will
generate a reset pulse to reset the system or trigger the IRQ 9 signal in order to tell your system that the watchdog
time is out.
Users could test watchdog function under ‘Debug’ program as follows:
C:>debug
o 2e 87 ;Extended Functions Enable Register
o 2e 87 ;Extended Functions Enable Register
o 2e 07 ;EFIR=EFER (Extended Functions Index Register)
point to Logical Device Number Reg.
o 2f 08 ;EFDR=EFIR+1,select logical device 8
o 2e f6 ;select CRF6
o 2f 08 ;update CRF6 with value 08H ,(8sec reset)
o 2e 30 ;select CR30
o 2f 01 ;update CR30 with value 01H
q