CHAPTER 1 INTRODUCTION
User’s Manual U14272EJ3V0UM
40
The instruction set can be further divided into the following four groupings:
(a) Load and store instructions move data between memory and general-purpose registers. They include RRI,
RI, I8, and RI64 types.
(b) Computational instructions perform arithmetic, logical, shift, and multiply and divide operations on values in
registers. They include RI, RRIA, I8, RI64, I64, RR, RRR, I8_MOVR32, and I8_MOV32R types.
(c) Jump and branch instructions change the control flow of a program. They include JAL/JALX, RR, RI, I8, and I
types.
(d) Special instructions are BREAK and Extend instructions. The BREAK instruction transfers control to an
exception handler. The Extend instruction extends the immediate field of the next instruction. They are RR
and I types. When extending the immediate field of the next instruction by using the Extend instruction, one
cycle is needed for executing the Extend instruction, and another cycle is needed for executing the next
instruction.
1.4.3 Data formats and addressing
The V
R
4181 uses the following four data formats:
•
Doubleword (64 bits)
•
Word (32 bits)
•
Halfword (16 bits)
•
Byte (8 bits)
If the data format is any one of halfword, word, or doubleword, the byte ordering can be set as either big endian or
little endian. However, the V
R
4181 only support the little-endian order.
Endianness refers to the location of byte 0 within the multi-byte data structure. Figure 1-6 show the configuration.
When configured as a little-endian system, byte 0 is always the least-significant (rightmost) byte, which is
compatible with Pentium
TM
and DEC VAX
TM
conventions.
In this manual, bit designations are always little endian.