Fanuc alarm: 971 - NMI OCCURRED IN SLC

An alarm condition occurred in the interface with an I/O unit. For PMC-
RA1, PMC-RA2, and PMC-RB, check that the PMC control module on
the main CPU board is conneted to the I/O unit securely. For PMC-RC,
check that the PMC control module on the option 3 board is connected
to the I/O unit is supplied with power and that the interface module is intact.