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A jumper labeled "2 485En" (J7) enables RS485 operation on the Serial2 port if the jumper cap is installed, and configures Serial2 for RS232 operation if the jumper cap is not installed. The hardware detects the start-bit of the transmission and automatically enables (on the fly) the RS485 transmitter. Any number of characters can be sent, and the transmitter will automatically re-trigger with each new character (or in many cases a "bit-oriented" timing scheme is used in conjunction with network biasing for fully automatic operation, including any Baud rate and/or any communications specification, eg. In general, all devices on a network should use the same phase, polarity, and baud rate clock signal. To interface devices that support synchronized serial interfaces, but are not configurable like the QScreen, determine the device’s requirements for clock phase and polarity and configure the QScreen’s CPHA and CPOL accordingly. Of the processor’s three synchronous SPI (Serial Peripheral Interface) ports, two are available for inter-processor communications on multi-processor systems, and the third is brought out to the Wildcard expansion bus. Pre-coded device drivers configure the SPI for a standard data format, and it is easy to customize a data format and baud rate for your application.

The specification allows for data transmission from one transmitter to one receiver at relatively slow data rates (up to 20K bits/second) and short distances (up to 50Ft. @ the maximum data rate). You might also consider operating the secondary serial port at a lower baud rate to relax the timing constraints. RS422 (differential) was designed for greater distances and higher Baud rates than RS232. Differential signals can help nullify the effects of ground shifts and induced noise signals that can appear as common mode voltages on a network. It is NOT necessary to introduce long delays in a network to avoid "data collisions." Because delays are NOT required, networks can be constructed, that will utilize the data communications bandwidth with up to 100% through put. By connecting pairs of these handshaking signals together, the terminal or PC can be made to think that the PDQ Board is always ready to send and receive data. RS485 cables typically consist of twisted pairs of wires with a characteristic impedance of 120 ohms, which helps to minimize signal reflections and interference.

Additionally, the adoption of Ethernet-based communication protocols in industrial automation systems has also influenced the evolution of RS485 cables, with some applications transitioning to higher-speed Ethernet connections for faster data transfer. Electronic data communications between elements will generally fall into two broad categories: single-ended and differential. When communicating at high data rates, or over long distances in real world environments, single-ended methods are often inadequate. RS232 (single-ended) was introduced in 1962, and despite rumors for its early demise, has remained widely used through the industry. In its simplest form, a pair of converters from RS232 to RS422 (and back again) can be used to form an "RS232 extension cord." Data rates of up to 100K bits / second and distances up to 4000 Ft. Its simplest implementation requires only three wires: one to transmit serial data, a second to receive serial data, and a third to provide a common ground reference.

Each serial port can be configured for the RS232 or RS485 protocol, and runs at standard baud rates up to 115,200 bits per second. You may use nonstandard baud rates if both devices support them. This connection may be used to limit the common-mode signal that can be impressed on the receiver inputs. In general if you are not connected to a modem the handshaking lines can present a lot of problems if not disabled in software or accounted for in the hardware (loop-back or pulled-up). Also, RS485 drivers are able to withstand "data collisions" (bus contention) problems and bus fault conditions. Systems of this type (4-wire, half-duplex) are often constructed to avoid "data collision" (bus contention) problems on a multi-drop network (more about solving this problem on a two-wire network in a moment). We have solutions to most problems that are encountered in this area. Suggestions are often made to deal with practical problems that might be encountered in a typical network. A true multi-point network consists of multiple drivers and receivers connected on a single bus, where any node can transmit or receive data. RS485 meets the requirements for a truly multi-point communications network, and the standard specifies up to 32 drivers and 32 receivers on a single (2-wire) bus.

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