Mitsubishi Electric MELSEC iQ-R Series Programming Manual page 124

Block START/END bit
This bit is a device or label to check whether the block is active.
Setting the bit to on can start the block and setting it to off can end the block.
If a program to start a block is not available or because the START/END of a block can also be controlled from the engineering
tool, this device or label can be used for debugging or test operation in units of block.
• When the set block starts, the block START/END bit is automatically turned on. While the set block is active, the block
START/END bit stays on.
• When the set block becomes inactive, the block START/END bit is automatically turned off. While the set block is inactive,
the block START/END bit stays off.
Ex.
M0 is specified in the block START/END bit of Block 1 (BL1).
(1) Block 1 (BL1) starts and M0 turns on.
(2) Block 1 becomes inactive and M1 turns off.
• When the block START/END bit is turned on while the set block is inactive, the block is started independently.
• When the block START/END bit is turned off while the set block is active, the block is ended.
The block START/END bit can also be turned on or off by the test operation of the engineering tool. ( GX Works3
Operating Manual)
When the block START/END bit is turned off to make the set block inactive, processing will occur as follows:
• Execution of the set block is stopped and the outputs of the step being executed are all turned off. However, the devices turned on by using the SET
instruction will not be turned off.
• If another block has been started by a block start step in the set block, the set block ends but the start destination block will remain active and continue
processing.
By changing the current value of BL or BL\S from watch window of the engineering tool, the status of a
block (START/END) or a step (active/inactive) can be changed.
Also, the status of the specified step (active/inactive) is changed from the menu [Debug]  [Control SFC
Steps]. ( GX Works3 Operating Manual)
8 SFC PROGRAM
122
8.4 SFC Information Devices
BL1
(1)
(2)
(1)
M0
(2)