Mitsubishi Electric MELSEC-Q Series Programming Manual page 172

Area to be overwritten
This section describes the area to be overwritten.
■Area to be changed
All programs of the target block are overwritten. Multiple blocks cannot be batch-written. In online change (inactive block), a
program (before change) in a programming tool is not verified with the program in the CPU module. Therefore, verifying an
SFC program in the programming tool with that in the CPU module beforehand is recommended.
■Change in signal flow memory
Signal flow memories of the target block all turn off.
■SFC information devices
The following SFC information devices can be added/changed/deleted.
• Block START/END bit
• Step transition bit
• Block PAUSE/RESTART bit
• Pause mode bit
• Number of active steps register
• Continuous transition bit
Before an SFC program is changed, the above devices are checked if they are within the device range. If any
of them are outside the device range, the online change (inactive block) cannot be performed.
■Available execution type
Online change (inactive block) can be executed to a scan execution type program (cannot be executed to a standby type
program).
■Changing the execution type of a program during online change (inactive block)
The execution type of a program being written by online change (inactive block) cannot be changed with Program control
instructions (POFF and PSCAN instructions).
■Availability depending on block status
The following table shows availability of online change (inactive block) depending on the block status at the start of writing.
Block status
*1
Inactive
Active
*1 For how to end processing of a block and set it to inactive, refer to Page 161 Block END methods.
*2 While SM321 is off, online change (inactive block) can be executed, regardless of the target block status immediately before the relay
turns off. Note when online change (inactive step) is executed while SM321 is off, the SFC program always starts in initial start mode,
regardless of settings configured in "SFC Program Start Mode" in the SFC tab of the PLC parameter dialog box and SM322 (SFC
program start status).
6 SFC PROGRAM EXECUTION
170
6.6 Operation at Program Change
Availability
Online change (inactive block) can be executed.
Online change (inactive block) cannot be executed.
However, while SM321 (Start/stop SFC program) is off, even when the block is active immediately before the relay turns off,
online change (inactive block) can be executed.
*2