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FX Series Programmable Controllers STL Programming 3
3-9
3.5.2 Single Signal Step Control
Transferring between active STL steps can be controlled by a single signal. There are two
methods the user can program to achieve this result.
Method 1 - Using locking devices
In this example it is necessary to program separate locking devices, and the controlling signal
must only pulse ON. This is to prevent the STL programs from running through.
The example shown below identifies the general program required for this method.
- S30 is activated when M0 is first pulsed ON.
- The operation of M1 prevents the sequence
from continuing because although M0 is ON,
the transfer requirements, need M0 to be ON
and M1 to be OFF.
- After one scan the pulsed M0 and the ‘lock’
device M1 are reset.
- On the next pulse of M0 the STL step will
transfer program control from S31 to the next
step in a similar manner. This time using M2 as
the ‘lock’ device because dual coils in
successive steps is not allowed.
- The reason for the use of the ‘lock’ devices M1
and M2 is because of the handshaking period
when both states involved in the transfer of
program control are ON for 1 program scan. Without the ‘locks’ it would be possible to
immediately skip through all of the STL states in one go!
Method 2 - Special Single Pulse Flags
Using the pulse contacts (LDP, LDF, ANP, etc.) and a special range of M devices (M2800 to
M3071) the same result as method 1 can be achieved. The special feature of these devices
prevents run through of the states, as only the first occurrence of the LDP instruction will
activate.
The example program below shows the necessary instructions.
- Assume S50 is already active.
- When X01 activates M2800, this in turn
activates the LDP M2800 instruction in
S50 and the flow moves on to step
S51.
- The LDP M2800 instruction in the
transition part of S51 does not execute
because this is the second occurrence
of M2800 in a pulse contact.
- When X01 next activates M2800, the
LDP instruction in S51 is the first
occurrence because S50 is now
inactive. Thus, control passes to the
next step in the same manner.
M1PLS
M0
S 30
S 31
M2PLS
M1
M2
M0
M0
S 50
S 51
M2800
M2800
LAD0
M2800
M2800
M2800
X001
SET S51
M2800
SET Snn
M2800
Do not use the
step control
device in a
pulse contact
within the main
program body.