Mitsubishi Electronics FX3G User Manual
274
FX
3S
/FX
3G
/FX
3GC
/FX
3U
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3UC
Series
Programming Manual - Basic & Applied Instruction Edition
10 Arithmetic and Logical Operation (
+, −, ×, ÷) – FNC 20 to FNC 29
10.2 FNC 21 – SUB / Subtraction
Related devices
1. Relationship between the flag operation and the sign (positive or negative) of a numeric value
→ For the flag operations, refer to Subsection 6.5.2.
Cautions
1. When using a 32-bit operation instruction (DSUB or DSUBP)
When specifying word devices, a 16-bit word device on the low-order side is specified first, and then a word device
with the subsequent device number is automatically set for the high-order 16 bits.
To prevent number overlap, it is recommended to always specify an even number, for example.
2. When specifying the same device in the source and destination
The same device number can be specified for both the source and the destination.
In this case, note that the addition result changes in every operation cycle if a continuous operation type instruction
(SUB or DSUB) is used.
(SUB or DSUB) is used.
Program example
1. Difference between the SUB instruction and the DEC instruction used by a program for
subtracting "1"
When SUB[P] is executed, "1" is subtracted from the contents of D0 every time X001 turns from OFF to ON.
SUB[P] instruction is similar to DECP instruction described later except the contents shown in the table below:
Device
Name
Description
M8020
Zero
ON : When the operation result is 0
OFF : When the operation result is other than 0
OFF : When the operation result is other than 0
M8021
Borrow
ON : When the operation result is less than
−32768 (in 16-bit operation) or −2,147,483,648 (in 32-bit operation)
OFF : When the operation result is not less than
−32768 (in 16-bit operation) or −2,147,483,648 (in 32-bit operation)
M8022
Carry
ON : When the operation result is more than 32767 (in 16-bit operation) or 2,147,483,647 (in 32-bit operation)
OFF : When the operation result is not more than 32767 (in 16-bit operation) or 2,147,483,647 (in 32-bit operation)
OFF : When the operation result is not more than 32767 (in 16-bit operation) or 2,147,483,647 (in 32-bit operation)
[D] SUB [P] instruction
[D] DEC [P] instruction
Flag (zero, borrow or carry)
Operates
Does not operate
O
per
ati
on
r
es
ul
t
16-bit
operation
operation
−(+1)=
←−2←−1←0←−32768
−32,768→+32,767→+32,766
−(−1)=
+32767
→0→+1→+2→
⎯
32-bit
operation
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→
⎯
Zero flag
−2, −1, 0, −32768
Borrow flag
Zero flag
−2, −1, 0, −2,147,483,648
Borrow flag
The most
significant bit of
data becomes
"1".
Zero flag
32767, 0, 1, 2
Carry flag
Zero flag
2,147,483,647, 0, 1, 2
Carry flag
Zero flag
−1, 0, 1
Zero flag
−1, 0, 1
The most
significant bit
of data
becomes "0".
FNC 21
SUB
D 0
K 25
D 0
X001
(D 0)
− 25→(D 0)
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