Control Data Cyber 170 State Hardware Reference Manual page 232

Maintenance Channel Programming
Maintenance Channel Programming
NOTE
Maintenance registers are numbered 0 through
63 from left to right.
Maintenance Channel
A PP in the IOU can perform any or all of the following operations through
the
maintenance channel (MCH) to each system element, such as the CP, IOU, and CM.
Initializing registers, controls, and memories.
Monitoring and recording error information.
0
Verifying error-detection and correction hardware.
The maintenance channel consists of the maintenance channel interface on
channel 17
,
a
maintenance channel interface in each system element, and a
set of intgrconnecting cables.
The IOU maintenance channel interface contains a selector that connects to one
of up to seven system elements. The IOU is element 0, and its maintenance
access control is internally connected to the selector. All other system
elements are assigned arbitrary element numbers.
A single cable connects each
maintenance access control to the selector. This arrangement results in a
radial connection that allows any system element to be shut down or removed
without affecting communication with the other elements.