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INSTRUCTION FORMATS
There are two main groups of instructions:
1.
Non-general instructions - Those for which the low-order bits specify a memory
address -- for example, memory reference instructions which may be subject to
address modification.
2.
General instructions - Those for which the low-order bits contain information to be
used by the instruction.
The notation I ( ) refers to the contents of an instruction word. General instructions may
be recognized by the fact that the three high-order bits, I (16-18), are all zeros. (When expressed
in octal notation, the general instructions start with
a~
in the high order position).
There is one format for non-general instructions and three for general instructions (register
transfer, status line and function driver, and C-register instructions).
' Non-general Instructions
The non-general, or memory reference, instructions have four fields:
18
Operation Code
Indirect Addressing Bit
Addressing Mode
13
12
11
10
9
I-24
---Partial
Memory Address
1
Position in the
Instruction Word, I
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