Teledyne T200, Operation Manual, Page: 140 / 425

Communications Setup and Operation Teledyne API
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Analyzer Operation Manual
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6.7.2. HESSEN
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. Teledyne API‟s
implementation supports both of these principal features.
The Hessen protocol is not well defined; therefore, while Teledyne-API‟s application is
completely compatible with the protocol itself, it may be different from implementations
by other companies.
6.7.2.1. HESSEN COM PORT CONFIGURATION
Hessen protocol requires the communication parameters of the T200‟s COM ports to be
set differently than the standard configuration as shown in the table below.
Table 6-4: 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 T200‟s COM ports, See Section 6.2.2.
To change the remaining COM port parameters listed in the table above, see Section
6.2.1, Table 6-1.
Note Ensure 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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