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Concept
Control register
Summary
A control register is a processor register that changes or controls the general behavior of a CPU or other digital device. Common tasks performed by control registers include interrupt control, switching the addressing mode, paging control, and coprocessor control.
When IBM developed a paging version of the System/360, they added 16 control registers to the design for what became the 360/67. IBM did not provide control registers on other S/360 models, but made them a standard part of System/370, although with different register and bit assignments. As IBM added new features to the architecture, e.g., DAS, S/370-XA, S/370-ESA, ESA/390, they added additional fields to the control registers. With z/Architecture, IBM doubled the control register size to 64 bits.
On the 360/67, CR0 and CR2 are used by address translation, CR 4-6 contain miscellaneous flags including interrupt masks and Extended Control Mode, and CR 8-14 contain the switch settings on the 2167 Configuration Unit.
Control Register 0 contains the address of the segment table for dynamic address translation.
Control register 2 is the Relocation exception address register.
CR4 is the extended mask register for channels 0-31.
Each bit is the 1/0 channel mask for the corresponding channel.
CR5 is reserved for the extended mask register for channels 32–63.
Each bit is the 1/0 channel mask for the corresponding channel.
CR6 contains two mode flags plus extensions to the PSW mask bits.
Control Register 8 contains the assignments of Processor Storage units 1–4 to central processing units (CPUs) and channel controllers (CCs).
Control Register 9 contains the assignments of Processor Storage units 5–8 to central processing units (CPUs) and channel controllers (CCs).
Control Register 10 contains the Processor storage address assignment codes.
Control Register 11 contains channel controller (CC) assignments.
CR12 contains I/O Control Unit Partitioning.
CR13 contains I/O Control Unit Partitioning.
CR14 contains indicators.
Official source
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