This is the I/O Bus Controller card for the High Level PIU, R320A and R320B.

This version of the I/O Bus Controller is used in High Level PIUs with the 4DP7APXPM144 and 4DP7APXPM155 PROM/RAM board.

The I/O Bus Controller card adapts the microprocessor bus to the signal and timing requirements of the PIU's I/O bus and A/D converter. It also performs diagnostic functions on the I/O section of the PIU, to prevent incorrect I/O card or point selection, to verify correct operation of the I/O clocks, to detect shorts between in the I/O lines, and to check the integrity of I/O address and data lines.

Revision 'D' or earlier may cause database corruption, use Rev 'E' or higher.