The link special relay (SB) is turned on/off depending on various factors during data link. Any error status of the data link can
be checked by using or monitoring it in the program.
Application of link special relay (SB)
By using link special relay (SB), the status of CC-Link IE TSN can be checked from HMI (Human Machine Interfaces) as well
as the engineering tool.
Ranges turned on/off by users and by the system
The following ranges correspond to when the link special relay areas (SB) are assigned from SB0000 to SB0FFF.
• Turned on/off by users: SB0000 to SB001F
• Turned on/off by the system: SB0020 to SB0FFF
List of link special relay (SB)
The following table lists the link special relay areas (SB) when they are assigned from SB0000 to SB0FFF.
Do not turn on or off areas whose Nos. are not on the following list or ranges turned on/off by the system.
Doing so may cause malfunction of the programmable controller system.
Clear communication error
Cyclic data receive status
Network type of own station
Module operation mode of
Station setting 1 of own
Station No. setting status of
Data link error status of own
CPU minor error status of
CPU moderate/major error
status of own station
CPU operating status of own
Received parameter error
Appendix 2 List of Link Special Relay (SB)
List of Link Special Relay (SB)
Clears the link special register areas related to communication errors (SW0074 to SW0077) to 0.
Off: Clear not requested
On: Clear requested (valid while on)
Clears the cyclic data receive status (SB0064).
While SB0014 is on, the cyclic data receive status does not turn on.
Off: Clear not requested
On: Clear requested (enabled while on)
Stores the network type of the own station.
On: CC-Link IE TSN
Stores the module operation mode of the own station.
Off: Online mode
On: Other than online mode
Stores the station type of the own station.
Off: Slave station (other than the master station)
On: Master station
Stores the station No. setting status.
Off: Station No. set
On: Station No. not set (local station only)
If parameters are set using the engineering tool, this relay is always off.
Stores the data link error status of the own station.
When this relay is turned on, the cause of the error can be checked with 'Cause of data link stop' (SW0049).
Depending on the link refresh timing, the update of 'Cause of data link stop' (SW0049) may be offset by one
(Also used in the CLPA conformance test.)
Stores the minor error status of the CPU module on the own station.
Off: No minor error
On: Minor error
Stores the moderate/major error status of the CPU module on the own station.
Off: No moderate/major error
On: Moderate/major error
Stores the operating status of the CPU module on the own station.
On: STOP, PAUSE, or moderate/major error
Stores the status of received parameter. (For the master station, this relay stores the parameter status of the