Table of Contents
Advertisement
9.05 WATCHDOG TIMER
The Watchdog Timer is extremely useful in embedded systems, where human supervision
is not required.
Jumper W25 must be installed to permit activation of the Watchdog. If jumper W25 is
removed, the Watchdog is disabled.
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 the first time (or at 290H or 390H
depending on the W21 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 290H or
390H), 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.
TABLE 9-2: Watchdog Timer Register
ADDRESS
190H, 290H or 390H: Bit 0
190H, 290H or 390H: Bit 1
Power Management
REGISTER
Read/Write
Watchdog enable
Read/Write
Watchdog refresh
9-6
Advertisement
Table of Contents
