Acnodes PCH 5120 C. WATCHDOG TIMER

14628 Central Blvd,

Chino, CA91710

tel:909.597.7588, fax:909. 597.1939

All r ights reserv ed. Product descr iption and produ ct specific ations

are sub ject to c hange without not ice. For latest product in formation,

please visit Acnode s’ we b si te a t ww w.acnodes. com.

PCH 5120

12.1” industrial Panel PC

IP67 rated fully enclosure

C. WATCHDOG TIMER

NOTE:

The followi ng discussion a pplies to DOS envi ronment. IEI sup port is contact ed or the

IEI website vis ited for specific drive rs for more sophisti cated operatin g systems, e.g.,

Windows an d Linux.

The Watchdog Timer is provide d to ensure th at standalone s ystems can alw ays recover from

catastroph ic conditions that cause th e CPU to crash . This conditi on may have occu rred by

external E MIs or a softwar e bug. When the CPU stops worki ng correctly, Watchd og Timer

either perfo rms a hardware reset (cold boot) or a Non-Maskable I nterrupt (NMI) to bri ng the

system back to a known sta te.

A BIOS function ca ll (INT 15H) is used to control the Watchd og Timer.

Call sub-fun ction 2 to set the time-o ut period of Watchdog Timer first. If the time -out value is

not zero, th e Watchdog Timer s tarts counting do wn. When the t imer value reac hes zero, the

system rese ts. To ensure that this reset conditi on does not occur, c alling sub-fun ction

2 must periodi cally refresh the Watchdog Timer. Howeve r, the watchdog time r is disabled if

the time-out value is set to zer o.

A tolerance o f at least 10% mus t be maintaine d to avoid unknow n routines wi thin the operat-

ing system (DOS ), such as disk I/O th at can be very time-c onsuming.

NOTE:

When exitin g a program it is nec essary to disable the Watchdog Timer, oth erwise the syst em

resets.