GMC-I Messtechnik GmbH 45
6.1 General
The instrument is equipped with an RS232, as well as an RS485 interface as standard equipment.
However, only one interface may be operated at any given time. If a LON interface has been installed
(optional), the RS485 interface is not included. See
chapter 5 on page 40 for electrical connections. If
the optional Profibus DP interface has been installed instead of the LON interface, the RS-485 and the
analog outputs are omitted. See the Profibus DP interface description for electrical connections.
•Char. format: 8 data bits, 1 parity bit, 1 stop bit
• Parity: even, odd, space, no
The following settings are required in order to fulfill the requirements set forth in the respective
standards:
– DIN draft 19244: even, if operated at a modem: no
– EN 60870: even
– Modbus: even, odd, no
RS-232
Depending upon the driver software, it may be necessary to install jumpers at the master, e.g.
DCD+DTR+DSR and RTS+CTS.
RS-485
If the RS485 interface is used, up to 32 instruments can be interconnected via the bus. In this case, all
ABC terminals are connected to one another in parallel. Wiring must be carried out from one instrument
to the next; star networks may not be implemented. For bus cables of greater than 5 meters in length,
the bus should be terminated at both ends with a surge impedance (e.g. 200 between A and B).
6.2 Communications Protocol
The communications protocol in accordance with DIN draft 19244, EN 60870 or the Modbus protocol
is used for communications between the field control and device levels. The A2000 utilizes only a sub
-
set of the functions defined in the protocol. Separate descriptions are available for each of the individual
communications protocols.
The following functions are not used: query acknowledgement for individual characters and transmis-
sion control by means of record sequence bit.
Time Response Characteristics
Ready to transmit/receive after start-up t
ber
> 5 s
Character delay time (A2000 transmitter) t
zvs
< 3 ms
Character delay time (Master) t
zvm
< 100 ms
Response delay time (A2000 transmitter) 10 ms < t
av
< 100 ms
Query waiting time after response from A2000 (master) t
aw
> 10 ms
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