Control Registers - IBM 5251 Series Maintenance Information Manual

Control Registers
Each display station contains three registers that the
controller can access. Each register is an address
pointer. The registers are named the cursor, address
counter, and the reference counter.
The cursor register controls the location of the cursor on
the display screen. The address counter register is used
to read and write data. The reference counter register is
used for moving data from one display area to another.
Theory 5251 MIM 4-19