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SYSTEM CONFIGURATION
31
2.8 Arithmetic Operation Section
(1) Outline
The MSM80C154S/MSM83C154S arithmetic operation section consists of
(1) an arithmetic operation instruction decoder, and
(2) an arithmetic and logic unit [ALU].
(2) Arithmetic operation instruction decoder:
Arithmetic operation instructions are passed to the instruction register (IR) and then to
the PLA where they are converted into control signals.
The control signals from the PLA are used to control ALU peripheral circuits and ALU
arithmetic operations (ADD, AND, OR, EOR).
(3) Arithmetic and logic unit [ALU]:
Upon reception of 8-bit data from one or two data sources the ALU processes that data
in accordance with control signals from the PLA. The ALU is capable of executing the
following processes:
• Additions and subtractions with and without carry
• Increments (+1) and decrements (–1)
• Bit complements
• Rotations (either direction with and without carry)
• BCD (decimal adjust)
• Carry, auxiliary carry, and overflow signal output
• Multiplications and divisions
• Bit detection
• Exchange of low and high order nibbles
• Logical AND, logical OR, and exclusive OR
If a bit-3 auxiliary carry (AC), a bit-7 carry (CY), or an overflow (OV) is generated as a
result of the arithmetic operation executed by the ALU, that result is set in the program
status word (PSW 0D0H).
CY
7
AC
6
F0
5
RS1
4
RS0
3
OV
2
F1
1
P
0
PSW(0D0H)
Figure 2-22 Program status word