Notification (J) message
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Description (see command description format info here)
Notification message in not a command, it is a message that the DS sends to the network host when one of the monitored I/O lines of the DS changes its state (for longer than 20milliseconds). The status of all lines is rolled into a single byte of data and sent out even when a single I/O line changes its state.
Notification messages are only generated when the data connection is in progress and are sent to the network host with which this data connection is established. Notification Destination (ND) setting defines which port on this network host notifications are sent to.
How notifications are sent (out-of-band, inband, etc.) is defined by several factors:
The value in each Notification message should be interpreted as a collection of binary bits, with each position corresponding to a certain I/O line of the DS. Bit positions are exactly the same as those of the Notification Bitmask (NB) Setting. Bit values correspond to the states of the I/O lines of Modules. Line states on the RS232 connectors of Serial Device Servers and Boards that incorporate RS232 transceivers are inverted relative to the states reported in the notification message.
Example: supposing, the following Notification message is sent*:
Decimal 27 converts to binary 00011011. This means that:
Notification messages are not commands so they do not require any reply from the receiving end.
If it is the DS that receives a Notification message from another DS, then the following happens:
The above means that the Notification message links RTS-CTS and DTR-DSR signals on two communicating DS: when the CTS input on one end changes its status the RTS output on the other end changes its status accordingly (same with the DTR-DSR pair).
* Encapsulation characters such as IEC, STX, CR are not shown.