The control registers provide for loading and storing control
information.
Two instructions, LOAD CONTROL and STORE CONTROL, are provided. LOAD CONTROL furnishes a means
of loading control information from main storage into
control registers; STORE CONTROL permits information
to be transmitted from control registers to main storage.
These instructions operate in a manner similar to LOAD
MULTIPLE and STORE MULTIPLE.
The structure provides for sixteen 32-bit registers for
control purposes. These registers are not part of addressable
storage.
One or more specific bit positions in control registers are
assigned to each function requiring register space. A model
may, however, furnish more control register bit positions
than required by the installed function. For example, a
model may provide register positions for more channel
mask bits than the number of channels installed. It depends
on the model and on the installed functions whether
additional unassigned control register bit positions are
furnished.
Only the general structure of the control register function
is described here; a description of the assignment and
meaning of register positions appears with the description