Instruction operands can be grouped into three classes, operands located in registers, immediate operands, and operands in storage.
A register operand can be located in general, floating-point, access, or control register. The register is identified by a four-bit field. The field containing the register operand is called the R field.
Immediate operands are contained within the instruction and can have 8, 16 or 32 bits. The field containing the immediate operand is called the I field. Dependent on the instruction the I field is either signed or unsigned.
A storage operand consists of an address and a length. The address of a storage operands can be specified in any of these ways:
The length of a storage operand can be:
The notation for storage operand addresses formed from multiple fields is as follows:
Dn(Bn)
Dn(Xn,Bn)
Dn(Ln,Bn)
The base registers Bn and the index registers Xn of a storage operand can be skipped. If Bn and Xn are skipped, a zero will be stored to the operand field. The notation changes as follows:
full notation | short notation |
---|---|
Dn(0,Bn) | Dn(Bn) |
Dn(0,0) | Dn |
Dn(0) | Dn |
Dn(Ln,0) | Dn(Ln) |