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Teledyne API - Model 200EH/EM Operation Manual Operating Instructions
149
6.15.4. USING THE M200EH/EM WITH A HESSEN PROTOCOL NETWORK
6.15.4.1. 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
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.
The following subsections 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
Instruments’ web site: http://www.teledyne-api.com/manuals/index.asp .
6.15.4.2. Hessen COMM Port Configuration
Hessen protocol requires the communication parameters of the M200EH/EM’s COMM ports to be set differently
than the standard configuration as shown in the table below.
Table 6-34: RS-232 Communication Parameters for Hessen Protocol
Parameter Standard Hessen
Data Bits 8 7
Stop Bits 1 2
Parity None Even
Duplex Full Half
To change the rest of the COMM port parameters and modes (see Section 6.11.8).
To change the baud rate of the M200EH/EM’s COMM ports (see Section 6.11.9.)
NOTES
Make sure that the communication parameters of the host computer are properly
set.
The instrument software has a 200 ms. latency before it responds to commands
issued by the host computer. Activating Hessen Protocol.
Operation via modem is not available over any COMM port on which HESSEN protocol
is active.
04521C (DCN5731)