Flachmann und Heggelbacher Docklight V2.2, User Manual

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Docklight V2.2 User Manual 07/2016 Copyright 2016 Flachmann und Heggelbacher GbR
Glossary / Terms Used
11.13 RS422
An RS422 communication link is a four-wire link with balanced line drivers. In a balanced
differential system, one signal is transmitted using two wires (A and B). The signal state
is represented by the voltage across the two wires. Although a common signal ground
connection is necessary, it is not used to determine the signal state at the receiver. This
results in a high immunity against EMI (electromagnetic interference) and allows cable
lengths of over 1000m, depending on the cable type and baud rate.
The EIA Standard RS422-A "Electrical characteristics of balanced voltage digital
interface circuits" defines the characteristics of an RS422 interface.
Transmitter and receiver characteristics according to RS422-A are:
Signal State Transmitter Differential
Voltage V
AB
Receiver Differential
Voltage V
AB
Mark (or logical 1) -6V to -2V -6V to -200mV
Space (or logical 0) +2V to +6V +200mV to 6V
Undefined -2V to +2V -200mV to +200mV
Permitted Common Mode Voltage V
cm
(mean voltage of A and B terminals with reference
to signal ground): -7V to +7V
11.14 RS485
The RS485 standard defines a balanced two-wire transmission line, which may be
shared as a bus line by up to 32 driver/receiver pairs. Many characteristics of the
transmitters and receivers are the same as
RS422 . The main differences between
RS422 and RS485 are
· Two-wire (half duplex) transmission instead of four-wire transmission
· Balanced line drivers with tristate capability. The RS485 line driver has an additional
"enable" signal which is used to connect and disconnect the driver to its output
terminal. The term "tristate" refers to the three different states possible at the output
terminal: mark (logical 1), space (logical 0) or "disconnected"
· Extended Common Mode Voltage (V
cm
) range from -7V to +12V.
The EIA Standard RS485 "Standard for electrical characteristics of generators and
receivers for use in balanced digital multipoint systems" defines the characteristics of an
RS485 system.
11.15 Send Sequence
A Send Sequence is a sequence that can be sent by Docklight. A Send Sequence is
specified by
1. an unique name (e.g. "Set modem speaker volume"),
2. a character sequence (e.g. "41 54 4C 0D 0A" in HEX format).
There are two ways to make Docklight send a sequence:
· Sending a sequence can be triggered manually by pressing the send button in the
Send Sequences list
(see
Main Window ).