DESIGN DECISIONS FOR THE PDP-11/60 MID-RANGE MINICOMPUTERS 325

Focal point of the hardware maintainability effort is the microdiagnostic unit. This single board tests the logic on five of the six processor boards. When faults are detected, an error code is displayed on light-emitting diodes (LEDs). A fault directory can then be used to determine which boards are to be replaced. The unit requires only a small portion of the internal machine (the microword sequencing) to be operational.

In addition, a number of on-board diagnostic aids are included in the CPU design. These include LEDs to display the contents of the next