Teknor Industrial Computers TEK-AT4LVG, Technical Reference Manual

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Installing and Working With System Components 7-11
7.05.4 WATCHDOG TIMER
The Watchdog Timer is extremely useful in embedded systems where human supervision
is not required.
The Jumper Watchdog is set by using W24 jumper. Its setting is given in Section 4-8
(Jumper Settings).
The Watchdog must also be enabled and refreshed by software. To enable the Watchdog
by software, first write "1" in bit "0" at address 190H (or at 290H or 390H depending on
the W16 jumper setting).
When enabled, the microprocessor must refresh the Watchdog. This is done by writing
alternatively "0" and "1" to bit 1 at address 190H (or at 290H or 390H), once every 1.6
seconds (or less) to verify proper software execution.
Following a reset, the Watchdog is always disabled.
If a hardware or software failure occurs such that the Watchdog is not refreshed, a reset
pulse is generated by the Watchdog to restart the processor.
F
The user program must provide the first access to address 190H (or at 290H or
390H depending on the W16 jumper setting), and must also include the refresh
routine. In addition, be certain to keep a mirror image of register 190H (or 290H
or 390H) when programming it. This is necessary since the register is a write-
only user register and, as a result, is not used by the system BIOS.