HP 16500A Setting Up page 24

If, at power-up, the HP 16500A CPU board finds a mainframe
Interface board in any one of its five card slots, it checks the expansion
frame interlace board to determine whether an HP16501A Expansion
Frame is present. If so, the CPU establishes a "link" between the rear
panels of the two frames,
which
then are displayed by the System
Configuration menu as a nine-slot system located on the HP 16500A
rear paneL
Figure 2-8. System Configuration with the HP 16501A
Turning On the HP 16500A/16501A
2-10
HP 16500A/16501A
Setting Up the System