Mitsubishi Electric MELSEC-Q Series User Manual page 41

4 SEQUENCE PROGRAM CONFIGURATION & EXECUTION
CONDITIONS
4
4 - 2
(2) Sequence program writing format
Programming for sequence programs is possible using either ladder mode, or list
mode.
(a) Ladder mode
• The ladder mode is based on the relay control sequence ladder.
Programming expressions are similar to the relay control sequence ladder.
• Relay symbolic language programming occurs in ladder block units.
A ladder block is the smallest unit of sequence program processing, with
the ladder beginning from the left bus and ending at the right bus.
Left bus a Contact
X0
0
X1 X2
Step No.
2
X4 X5
8
Y24
X0 to X5 : Indicate inputs.
Y20 to Y24 : Indicate outputs.
(b) List mode
The list mode uses dedicated instructions instead of the contact symbols,
coil symbols, etc., used in the ladder mode.
Contact a, contact b and coil instructions are as follows:
• a contact ............LD, AND, OR
• b contact ............LDI, ANI, ORI
• coil......................OUT
(2) Program processing
Sequence programs are processed in order, beginning from step 0 and ending at
the END/FEND instruction.
Processing of ladder mode ladder blocks begins from the left bus, and proceeds
from left to right. When one ladder block is completed, processing proceeds
downward to the next ladder block.
[Ladder mode]
Left to right
1) 2) 7) 8)
X0 X1 X5 X6
0
3) 4)
5)
X2 X3
Top to
bottom
6)
X4
10
Numbers 1) to 11) indicate the processing
order of the sequence program.
Fig.4.2 Sequence Program Processing
b Contact Coil (output)
X3
Fig.4.1 Ladder Block
9)
10)
X7
Y10
Executed in
order, beginning
from step 0 to
the ending at
the END
11)
END instruction.
MELSEC-Q
Right bus
Y20
Y21
Y22 Ladder blocks
Y23
Y24
[List mode]
0 LD X0 1)
1 AND X1 2)
2 LD X2 3)
3 AND X3 4)
4 ORB 5)
5 OR X4 6)
6 AND X5 7)
7 AND X6 8)
8 AND X7 9)
9 OUT Y10 10)
10 END 11)
Step No.
4 - 2