Specifications

Glossary
D-10
nonmaskable interrupt: An interrupt that can be neither masked by the
interrupt mask register (IMR) nor disabled by the INTM bit of status
register ST0.
NPAR: Next program address register. Part of the program-address genera-
tion logic. This register provides the address of the next instruction to the
program counter (PC), the program address register (PAR), the micro
stack (MSTACK), or the stack.
O
operand: A value to be used or manipulated by an instruction; specified in
the instruction.
operand-fetch phase: The third phase of the pipeline; the phase in which
an operand or operands are fetched from memory. See also pipeline ;
instruction-fetch phase ; instruction-decode phase; instruction-execute
phase .
output shifter: 32- to 16-bit barrel left shifter. Shifts the 32-bit accumulator
output from 0 to 7 bits left for quantization management, and outputs
either the 16-bit high or low half of the shifted 32-bit data to the data write
bus (DWEB).
OV bit:
Overflow flag bit. Bit 12 of status register ST0; indicates whether the
result of an arithmetic operation has exceeded the capacity of the
accumulator.
overflow (in a register): A condition in which the result of an arithmetic
operation exceeds the capacity of the register used to hold that result.
overflow mode: The mode in which an overflow in the accumulator causes
the accumulator to be loaded with a preset value. If the overflow is in the
positive direction, the accumulator is loaded with its most positive
number. If the overflow is in the negative direction, the accumulator is
filled with its most negative number.
OVM bit:
Overflow mode bit. Bit 11 of status register ST0; enables or
disables overflow mode. See also
overflow mode .
P
PAB: See program address bus (PAB).
PAR: Program address register. A register that holds the address currently
being driven on the program address bus for as many cycles as it takes
to complete all memory operations scheduled for the current machine
cycle.