24 GMC-I Messtechnik GmbH
Note:
Interfaces (9) FIELD1 and (12) RS 485 (RS 485/1 for V3) are wired in parallel [see section
6. , “Connections Overview,”]. Using different protocols at the same time may result in errors
and bus interference.
The assignment for terminal (12) is printed in the SMARTCONTROL housing as A through C, and the conductors
are identified as 1 through 3 at the plug. A/1 (+), B/2 (-), C/3 (equipotential bonding).
Warning:
The Mod-Bus specification defines power supply (A –, B +) differently than the RS 485
specification (A +, B –).
Before connecting, determine which specification applies to the device to be connected!
Note:
Do not use terminal C (data ground) if the modules are supplied with power from the
SMARTCONTROL! This terminal is used exclusively to compensate for extraneous voltages from
other devices. It is thus not suitable for supplying power to the devices!
SMARTCONTROL
Module with External
Power Supply
Module with Supply Power from the
SMARTCONTROL
A
Data +
Data +
B
Data –
Data –
C
C
---
V +
---
V +
V -
---
V -
Topology: Under no circumstances may branches be laid with lengths of more than 2 meters.
Note:
Wiring is always looped through 1:1 from module to module.
The RS 485 bus has to be terminated at its ends with two resistors. In the case of short
distances (< 10 m), termination can be omitted. In the case of larger installations,
termination must be carefully executed: under no circumstances may bus voltage drop to
below 0.3 V. Under normal conditions, termination can be set up directly on the PCB with
the green JP4 jumper [see item (13) in section 6. , “Connections Overview,”] (220/110
Ohm). In special cases, lower resistance values are required (must be laid out correctly by
qualified personnel).
8.1.4.
ASCII Fieldbus Modules
Fieldbus modules which communicate via the ASCII protocol can be connected to terminals (9) and (12) [see
section 6. , “Connections Overview,”]. Firmware with option AA is required to this end [see section 9.1. ,
“Firmware Options”].
Please note that the two interfaces are parallel connected.
Supported baud rates: 1200, 2400, 4800, 9600, 19,200, 38,400 and 57,600 baud.
