Instructions - IBM 4300 Manual

more. Thus, unlike SUBTRACT, COMPARE can
cause no overflow.
Logical comparison of two operands is
performed byte by byte, in a left-to-right sequence.
The operands are equal when all their bytes are
equal. When the operands are unequal, the
comparison result is determined by a left-to-right
comparison of corresponding bit positions in the
first unequal pair of bytes: the zero bit in the first
unequal pair of bits indicates the low operand, and
the one bit the high operand. Since the remaining
bit and byte positions do not change the
comparison, it is not necessary to continue
comparing unequal operands beyond the first
unequal bit pair.
Instructions
The general instructions and their mnemonics,
formats, and operation codes are listed in the figure
"Summary of General Instructions." The figure
also indicates when the condition code is set and
the exceptional conditions in operand designations,
data, or results that cause a program interruption.
7-4 IBM 4300 Processors Principles of Operation
A detailed definition of instruction formats,
operand designation and length, and address
generation is contained in the section
"Instructions" in Chapter 5, "Program Execution."
Exceptions to the general rules stated in that
section are
explici~ly
identified in the individual
instruction descriptions.
Several instruction descriptions in this chapter
contain references to other CPUs, even though the
ECPS:VSE mode makes no provision for
multiprocessing, so as to permit the writing of
problem-state programs that are compatible with
multiprocessing configurations of System/370 (see
the section "Problem-State Compatibility" in
Chapter 1, "Introduction").
Note: In the detailed descriptions of the individual
instructions, the mnemonic and the symbolic
operand designations for the assembler language
are shown with each instruction. For LOAD AND
TEST. for example, LTR is the mnemonic and R
l'
R
2
the operand designation.