Modules And Accessories
3.105
SI-700 - EIA-232/EIA-485 Interface Module
Part Number
SI-700
(Interface EIA-232/EIA-485)
Description
This module converts the electrical characteristics of the communication signal from the EIA-232
specification to the EIA-485 specification. Due to the fundamental differences between the EIA-232
and the EIA-485, the first option EIA-232 is used in peer-to-peer applications) this module was
implemented to work automatically. No control signal is necessary to manage the bus contention on
the EIA-485 side. It is necessary to connect the transmission and reception lines on both sides to
make the interface work.
The converter circuit provides signal isolation to grant a safe connection between two systems. This
module was designed to use the DFI/LC platform. No power supply was embedded in the board. It
uses the +5Vdc lines from the IMB bus to energize the circuit.
Figure 3.66 - SI-700 Interface RS232/RS485
Interface Settings
There is two interface settings located on the front panel to adapt this interface to the applications:
RS232 Mode and RS485 Bus Terminator.
- RS232 Mode: Half-Duplex/Full-Duplex
The RS232 Mode setting adapts the use of RS232/RS485 Interface to the communication driver at
the RS232 side. Normally interfaces of this type connect unidirectional buses with a bi-directional
bus. The unidirectional bus will be able to present the Full Duplex features caused by transmission
message reflection (echo). If the driver used does not treat properly the reception and the
transmissions messages simultaneously, either disabling the reception or discarding the reflected
message, it will be necessary to select the Half-Duplex option. If the reflected message doesn’t
disturb the applications, you can select the Full-Duplex option.
- RS485 Bus Terminator: On/Off
The RS485 is a Multi-Drop type bus. The transmitter driver is put in the high impedance (Hi-Z) state
when there is no message to transmit. Therefore, the RS485 bus requires a bus terminator to
prevent noise problems during the idle state of the RS485.
For the proper line impedance matching it is necessary to activate only one terminator by bus.
Leave the other terminators deactivated.
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