4 -3
Ladder Diagram
Mnemonic code
X0
Y0
Y1
Y0
X1
ORG X 0 ---------------------
○
a
OUT Y 0 ---------------------
○
b
OUT Y 1 ---------------------
○
c
ORG X 1 ---------------------
○
d
OUT Y 0 ---------------------
○
e
N times scan
Scan Time t
N+1 times scan
a
b
c
d
e
X0
X1
Y0
A
Y0
Y0
Y1
Y1
A : The internal accumulator of PLC
a
b
c
d
e
Besides the TU/TD instructions which can detect the status change of reference operand, FBs-PLC also provides
the instructions to detect the change of node status (power flow). For details please refer the descriptions of FUN4
(DIFU) and FUN5 (DIFD) instructions at chapter 7.
4.2.2
OPEN and SHORT Contact
The status of OPEN and SHORT contact are fixed and can’t be changed by any ladder instructions. Those two contacts
are mainly used in the places of the Ladder Diagram where fixed contact statuses are required, such as the place where
the input of an application instruction is used to select the mode. The sample program shown below gives an example of
configuring an Up/Down counter (UDCTR) to an Up counter by using the SHORT contact.
ORG
X 0
LD SHORT
LD X
1
FUN 7
CV:
R
0
X0
X1
7.UDCTR
CV :
PV :
CK
U/D
CLR
R
0
10
R
CUP
PV:
R
10