Digital Equipment DECstation 5000/100 Series, Maintenance Manual

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15 8 7 6 5 4 3 2 1 0
+------------+----+----+-----+-------+-----+-----+----+
|
IM | KX | SX | UX | KSU | ERL | EXL | IE |
+------------+----+----+-----+-------+-----+-----+----+
8 1 1 1 2 1 1 1
The (CU) coprocessor usability field is a 4-bit field that
individually controls the usability of each of the four
coprocessor unit numbers (1 = usable, 0 = unusable).
Coprocessor zero is always usable in kernel mode,
regardless of the setting of the CU0 bit.
The (RP) reduce power enables reduced-power operation by
reducing the internal clock frequency.
The (FR) floating-point register enables additional floating-
point registers (0-16 registers; 1-32 registers).
The (RE) reverse endian when set reverse byte orientation
in User mode.
The (DS) diagnostic status field is an implementation-
dependent 9-bit diagnostic status field that is used for
self-testing and checking of the cache and virtual memory
system. See ‘‘Diagnostic Status Field’’ for a detailed
description of the DS field.
The interrupt mask field (IM) is an 8-bit field that controls
the eight external, internal, coprocessor, and software
interrupts (0 = disable, 1 = enable). If interrupts are
enabled, an external interrupt occurs when corresponding
bits are set in both the interrupt mask field of the SR and
the interrupt pending (IP) field of the cause register.
The (KX) enables 64-bit addressing in Kernel mode.
The (SX) enables 64-bit addressing and operations in
supervisor mode.
The (UX) enables 64-bit addressing and operations in user
mode.
The (KSU) Mode (10-User, 01_supervisor, 00-Kernel)
The (ERL) Error level (0-normal, 1-error)
The (EXL) Exception level (0-normal, 1-exception)
The (IE) Interrupt Enable (0-disable, 1-enable)
E–12 CPU and System Registers