Specifications

Little Board/P5i Technical Manual
3–28
The following simple assembly language routine illustrates how to control the watchdog timer using the
Ampro ROM-BIOS function that has been provided for this purpose:
;----------------------------------------------------------
; Watchdog timer control program
;----------------------------------------------------------
MOV AH,0C3h ; Watchdog Timer BIOS function
MOV AL,nn ; Use “00” to disable, “01” to enable
; timer.
MOV BX,mm ; Selects time, in seconds
;(00-FFh; 1-255 seconds)
INT 15h
Ampro provides a simple DOS program that can be used from the command line or in a batch program to
manage the watchdog timer. It is called WATCHDOG, and is described in the Ampro Common Utilities
manual.
Note
Some operating systems, including some versions of DOS, turn off
the real-time clock alarm at boot time. If your OS does this, make
sure that your application program enables the alarm function
using this BIOS call.
3.16 POWERFAIL MONITOR
A hard reset is generated by a powerfail circuit if power falls below 4.4V.
If you have jumpered W20, the power management circuitry generates a power-fail Non-Maskable
Interrupt (NMI) if the power falls below 4.7V.
When an NMI occurs, the BIOS detects the NMI and displays the message “Power Fail NMI” on the
console. At this point you have two options via the keyboard. You can mask the NMI and continue (the
PC architecture provides a mask bit for the non-maskable interrupt), or reboot the system.
If you want to do something else with the NMI, you must provide your own power fail NMI handler and
patch the NMI interrupt vector address to install it.