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LabVIEW drivers - FLOW-BUS chained command utility


The Bronkhorst FLOW-BUS protocol doesn't only provide commands to read the many device parameters of over 25 different devices, it also allows to combine commands into a single command using the technique of chaining. So instead of having several commands for reading a set of parameters from a particular device these commands can be combined. The reason to do this is to shorten the size of the message(s) that must be written to that device as well as the size of the message that must be written by that device in reply to the command. And in serial communication a shorten message means less time.

The way that commands are chained depends on the parameters being organized into groups called processes. The FLOW-BUS protocol uses the first bit (MSB) of the process number and the parameter number (e.g. parameter number within that process) to indicate that either the process or the parameter is chained. If there are commands for different processes they can be chained at process level. If there are commands for different parameters within the same process they can be chained at parameter level.

The rules for chaining command are described in the instruction manual 'RS232 interface with FLOW-BUS protocol for digital multibus Mass Flow / Pressure instruments' (Doc. no. 9.17.027Q).

Program description

The presented utility (flowbus offers an easy way to create (chained) parameter request commands using the FLOW-BUS RS232 ASCII protocol. The requirements to create commands can be entered in an easy left-to-right manner:

  1. The address of the device
    The address of a device is 2 more than the channel number found for that device through FlowDDE.
  2. The availability of parameters (which depends on the chosen device)
    After selecting the device type, either automatically or manually, the availability of the first 200 parameters can be set and the availablity of the remaining parameters can be checked.
  3. The list of requested parameters
    Any number of parameters can be selected but a very long command will also generate a very long response and what's more a very complex response.

With this requirements set a command can be created. For each parameter, as defined for FlowDDE, the actual process and parameter number as well as the required chaining bit(s) and data type will be selected.

If the device is connected to the selected serial port it can also be tested.

If there is any error while communicating with the device, the utility will show the corresponding error message. If there is a response from the device it will be shown and in the case of easy commands, or rather commands that request only a single parameter, the value of the response will be shown separately.


This file includes:

  • flowbus the abovementioned sample program
  • flowbus cc.chm the related helpfile
  • bronkhorst ascii.llb a library of files for use with the utility
  • bronkhorst ascii module.llb a library of files for using the RS232 ASCII protocol


  • All VIs have been created with LabVIEW 2011 SP1 Professional Development System
  • The instruction manual 'Operational instructions for digital Multibus Mass Flow / Pressure instruments' (Doc. no. 9.17.023V) shows there are even 35 different device types

See also


Bart Boshuizen, 2012/09/27


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