Teknor Industrial Computers PCI-993, Technical Reference Manual

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Power Management 14-3
14.03 POWER FAIL DETECTION CIRCUIT
The Power Failure Detector always monitors:
• The backup battery to warn of a low battery condition, and
• The +5V power supply to detect when it falls below 4.75V.
If either of the two above conditions occur, the PFO (Power Fail Output signal) goes
low. In the case of the +5V power supply, a reset will result as explained in the
previous section (14.02.2). In the case of the low battery, what happens will depend on
the setting of the W13 jumper and user-defined algorithm.
The W13 jumper, when shorted, will generate a NMI (Non Maskable Interrupt),
through the IOCHK* line, when the PFO goes low. In turn, this NMI may be serviced
by an interrupt handler to locate the source and notify the user or the system.
If the W13 jumper is left open, no NMI is generated, however an algorithm could be
used to detect a low battery condition and respond accordingly.
A low battery condition is detected, in any case, by polling bit 3 at TEKNOR’s I/O base
address register (190H, 290H or 390H, depending on W9 jumper setting): If this bit
reads “1”, then the battery voltage is good; if it reads “0”, then it is in a low condition
(below 2.9V, typical).
Jumper locations and settings are illustrated in Section 2.