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Operating Instructions Teledyne API Model T360/T360M Operation Manual
162
4.15.4. Using the T360 with a Hessen Protocol Network
4.15.4.1. 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 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 subs 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 .
4.15.4.2. HESSEN COM PORT CONFIGURATION
Hessen protocol requires the communication parameters of the T360’s com ports
to be set differently tha The standard configuration as shown in the table below.
Table 4-28: RS-232 Com 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 com port parameters. See Section 4.11.5.
To change the baud rate of the T360’s com ports, see Section 4.11.10.
NOTE
Ensure that the communication parameters of the host computer are also properly set.
Further note that 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.
07272B DCN6552