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On-the-fly commands are used to change the serial port configuration of the DS as needed (i.e. "on the fly"). Serial port configuration made through the on-the-fly commands overrides the permanent one, defined by the serial port settings of the DS. The difference between the changes made using on-the-fly commands and changes made through altering DS settings is that, unlike serial settings, on-the-fly commands have immediate effect and do not require the DS to be rebooted in order for the new values to be recognized.
With on-the-fly commands enabled, the serial port of the DS is always setup as required by the PC application that communicates with this DS through the VSP. When the PC application opens the VSP (or some communications parameters are changed) the application informs the VSP about required changes* and the VSP relates this information to the DS by sending on-the-fly commands.
Additionally, on-the-fly commands are used by the VSP to control the RTS and DTR outputs of the DS serial port. The status of the CTS and DSR input of the DS serial port can be passed to the VSP too- this is done using so-called "notification messages". For more information see handling of RTS, CTS, DTR, and DSR signals.
On-the-fly commands drop-down box provides four choices:
In general, we recommend you to keep on-the-fly commands enabled (unless there are some special reasons preventing you from doing so). Enabling on-the-fly commands keeps the serial port setup of the DS "in sync" with the requirements of the software application using the VSP.
As for choosing between out-of-band and inband modes, follow these recommendations:
Out-of-band commands work most of the time, especially when the PC (running VSP) and the DS are located on the same network segment**. Out-of-band commands may not work very well or not work at all for the remote Device Servers located behind the routers, firewalls, etc***. This is because:
If you encounter one of the above situations then you should use inband on-the-fly commands or not use on-the-fly commands at all!
There is one other reason why out-of-band commands may not be suitable- this is when on-the-fly commands must be synchronized with the data sent by the VSP. For more information see synchronization issues.
* This is standard for Windows COM ports.
** The definition of the network segment implies that there are only network hubs (and no routers, bridges, firewalls, etc.) between the PC and all other devices on the segment.
*** Here we touch on a very complicated subject. Modern routers offer a bewildering array of setup options. We will attempt to cover this in details in our upcoming white papers.