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Teledyne API – T101 Operation Manual Remote Operation
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5.1.4. USING THE T101 WITH A HESSEN PROTOCOL NETWORK
5.1.4.1. 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 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.
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 API web site:
http://www.teledyne-api.com/manuals/index.asp .
5.1.4.2. Hessen COMM Port Configuration
Hessen protocol requires the communication parameters of the T101’s COMM ports to be
set differently than the standard configuration as shown in the table below.
Table 5-6. Hessen RS-232 Communication Parameters
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 4.10.8.
To change the baud rate of the T101’s COMM ports, see Section 4.10.9.
NOTE
Make sure that the communication parameters of the host computer are also properly
set.
Also, the instrument software has a 200 ms. latency 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.
07266B DCN6485