Mitsubishi Electric MELSEC FX3U - Page 290

288
FX3G/FX3U/FX3UC Series Programmable Controllers
Programming Manual - Basic & Applied Instruction Edition
10 Arithmetic and Logical Operation ( + , − , × , ÷ ) – FNC 20 to FNC 29
10.2 FNC 21 – SUB / Subtraction
Program example
1. Difference between SUB instruction and DEC instruction caused by a program for
subtracting "1"
"1" is subtracted from the contents of D0 every time X001 turns ON from OFF.
SUB[P] instruction is similar to DECP instruction described later except the contents shown in the table
below:
[D] SUB [P] instruction [D] DEC [P] instruction
Flag (zero, borrow or carry) Operates Does not operate
Operation result
16-bit
operation
−(+1)=
←−2←−1←0←−32768 −32,768→+32,767→+32,766
−(−1)=
+32767→0→+1→+2→⎯
32-bit
operation
−(+1)=
←−2←−1←0←−2,147,483,648 −2,147,483,648→+2,147,483,647→+2,147,483,646
−(−1)=
+2,147,483,647→0→+1→+2→⎯
S D
S D
S D
S D
FNC 21
SUBP
D 0 K 1 D 0
X001
(D 0)
− 1 → (D 0)
FNC 25
DECP
D 0
X001
(D 0)
− 1 → (D 0)
S 1  S 2  D 