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16. AC POWER FAIL
The ZT 8904 supports AC power-fail detection as a means for giving the application
advanced warning of an impending power failure. The advanced warning may be used
by the application for performing operations such as saving critical data and entering a
dormant state.
The ZT 8904 requires a transformer-isolated AC voltage of no more than 30 V from the
same source that provides the system power. Ziatech's optional AC wall transformer
(ZT 90071) meets these requirements. The wall transformer is connected to the J3
frontplane connector, as shown in the following figure. The pin assignments for
connector J3 are given in Appendix B, "
Specifications
."
AC Wall Transformer Installation
In operation, a non-maskable interrupt is generated when AC power falls below
95 VRMS. The non-maskable interrupt must be enabled through jumper selection (W9).
The application software must include a non-maskable interrupt service routine to
perform the following:
•
Determine if the AC power fail is the source of the interrupt request. The three
sources of non-maskable interrupts are AC power fail, STD bus NMIRQ*, and Parity
Error.
•
Preserve any critical information into Flash memory, either for failure analysis or for
system restart.
•
Place the CPU in a dormant state using a halt instruction or a looping sequence that
is not reading or writing critical data to memory or I/O.
