Teledyne M300EM General Overview Of Hessen Protocol, Hessen Comm Port Configuration

Teledyne API – Technical Manual - Model 300E Family CO Analyzers Remote Operation

8.6.USING THE M300E/EM WITH A HESSEN PROTOCOL NETWORK

8.6.1.GENERAL OVERVIEW OF HESSEN PROTOCOL

The Hessen protocol is a multidrop protocol, in which several remote instruments are connected via a common communications channel to a host computer. The remote instruments are regarded as slaves of the host computer. The remote instruments are unaware that they are connected to a multidrop bus and never initiate Hessen protocol messages. They only respond to commands from the host computer and only when they receive a command containing their own unique ID number.

The Hessen protocol is designed to accomplish two things: to obtain the status of remote instruments, including the concentrations of all the gases measured; and to place remote instruments into zero or span calibration or measure mode. API’s implementation supports both of these principal features.

The Hessen protocol is not well defined, therefore while API’s application is completely compatible with the protocol itself, it may be different from implementations by other companies.

NOTE

The following sections describe the basics for setting up your instrument to operate over a Hessen

Protocol network.

For more detailed information as well as a list of host computer commands and examples of command and response message syntax, download the Manual Addendum for Hessen Protocol from the Teledyne API web site: http://www.teledyne-api.com/manuals/.

8.6.2.HESSEN COMM PORT CONFIGURATION

Hessen protocol requires the communication parameters of the M300E/EM Analyzer’s COMM ports to be set differently than the standard configuration as shown in Table 8-6.

Table 8-6: RS-232 Communication Parameters for Hessen Protocol

PARAMETER	STANDARD	HESSEN
Baud Rate	300 – 19200	1200
Data Bits	8	7
Stop Bits	1	2
Parity	None	Even
Duplex	Full	Half

To change the baud rate of the M300E/EM’s COMM ports, see Section 8.1.3.

To change the rest of the COMM port parameters listed in the Table 8-6.Also see Section 8.1 and Table 8-1.

Note

Make sure that the communication parameters of the host computer are also properly set.

Also, the instrument software has a 200 ms latency period before it responds to commands issued by the host computer. This latency should present no problems, but you should be aware of it and not issue commands to the instrument too frequently.

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