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Interface
In this way, the multiplexer master acts as a transparent gateway between the service station (typically a
PC with suitable software, see section 2.3.2) and the field devices. The service station is able to communi-
cate with up to 31 multiplexer master via up to 38400 baud R S485 connection. Because each master is
able to communicate with 256 field devices, up to 7936 field devices are controlable over a singl e RS485
interface.
HART
As a digital communication system for servicing and configuration purposes, the HART protocol is suppor-
ted by many field devices with conventional analogu e 4m A. . .2 0mA current loops. The HART signal is
thus modulated on the analogue current as an FSK signal (see section 2.2). The modulator/demodulator
circuitry (Modem) required for this is integrated in the multiplexer. Only one HART transmitter can be con-
nected at each multiplexer HART connection (no "multidrop" functionality).
Special procedures in respect to HART communication:
•
On the host side (RS 485) always the long frame address is used (except for command 0).
•
On the field devices side, either the short address or the long frame address is used, depending on
necessity.
•
The operating modes "Primary Master" and "Secondary Master" and the corresponding time responses
are supported on the field device side.
•
On the host side, only the commands 0 ... 3 and 1 1. . .13 are accepted from the secondary host. Other
commands are not accepted/are ignored.
•
Commands to connected field devices are only accepted by the primary host.
•
Extended messages and messages in the Burst Mode are recognised and used, but not generated by
the multiplexer itself.
•
An answer buffer is available for a delayed message response. This can be used to intermediately store
a message, the command for which requires a long execution time.
Loop construction/REBUILD (Software function)
On power-up, the device searches the multiplexers in the multiplexer table for the connected HART field
devices (commands 0 and 4
be carried out by the connected service station, as is necessary, for example, in communication with newly
connected HART field devices. The duration of this function depends on the number of connected multiple-
xer slaves and HART field devices and also on the type of loop search (see command 153) and the permis-
sible number of message repeats. With 16 HART devices (e.g. by using only one master without slaves) the
duration is between 1 5s and 3 0s. The number of permissible message repeats is set to "2" in the factory
setting and the loop search type to "single analogue".
During the REBUILD phase, only certain read commands are accepted from the service station (commands
0, 1, 2, 3, 11, 12, 13, 48, and 129). All other commands are followed by the response "Busy" (Code 32, see
section 5.3.2), until the REBUILD phase ends.
Cyclic data interrogation/SCAN (software function)
The multiplexer can read cyclic data from up to 31 transmitters. In this case the SCAN option must be set
for the transmitter (command 137) and the SCAN function activated in the multiplexer (command 149,
function 1). Which data is transferred is determined by the "SCAN command" option (command 147).
If the SCAN function is activated, the transmitters, on which the SCAN option is activated are regularly chek-
ked for data. In this case, the SCAN command is executed, with which one or more variables are read from
the transmitter. If a field device does not respond, it is designated as having "disappeared" (see command
129), but it remains in the search list (i. e., it is searched for again on the next run sequence). If a device
has disappeared, but responds correctly on the next search command, it is then listed as "appeared". If,
instead of this, another device has answered, then the status "mismatched" is assigned.
1. Command 4 is additionally used on transmitters which only support the old HART specifications up to 4.
Subject to reasonable modifications due to technical advances.
10
Pepperl+Fuchs Group • Tel.: Germany (06 21) 7 76-0 • USA (330) 4 25 35 55 • Singapore 7 79 90 91 • Internet http://www.pepperl-fuchs.com
1
) and generates the internally required access tables. This function can also
HART Multiplexer Master KFD2-HMM-16
Copyright Pepperl+Fuchs, Printed in Germany
Product description
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