Specifications

8–2 Altera Corporation
Nios II Processor Reference Handbook October 2007
Word Formats
R-Type
The defining characteristic of the R-type instruction-word format is that
all arguments and results are specified as registers. R-type instructions
contain:
■ A 6-bit opcode field OP
■ Three 5-bit register fields A, B, and C
■ An 11-bit opcode-extension field OPX
In most cases, fields A and B specify the source operands, and field C
specifies the destination register. Some R-Type instructions embed a
small immediate value in the low-order bits of OPX.
R-type instructions include arithmetic and logical operations such as add
and nor; comparison operations such as cmpeq and cmplt; the custom
instruction; and other operations that need only register operands.
The R-type instruction format is:
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
ABC OPX OP