Octagon PC-500, User Manual

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17-1
PC-500 user’s manual Watchdog timer and hardware reset
Chapter 17:
Watchdog timer and hardware reset
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Description
The watchdog timer is a fail-safe against program crashes or processor
lockups. It times out every 1.6 seconds (1.6 sec. typical, 1.00 sec. min.,
2.25 sec. max.) unless reset by the software. The watchdog timer can be
controlled through the enhanced INT 17h interface which is a built-in
function on the PC-500.
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Enhanced INT 17h function definitions
This section provides definitions for the following functions: Enable
watchdog, Strobe watchdog, and Disable watchdog.
Enable watchdog
Function: fdh
Subfunction: 01h
Purpose: To enable the watchdog.
Calling registers: AH fdh
AL 01h
DX ffffh
Return registers: None
Comments: This function enables the watchdog. Once the
watchdog is enabled, it has to be strobed at a period
of not less than 1.6 seconds or until the watchdog is
disabled. Otherwise, a system reset will occur.
Programming example:
/* Inline assembly code for Borland C++ 3.1 */
asm {
mov
ax,0fd01h
mov dx,0ffffh
int 17h
}