Many terminals and PCs, however, do rely on hardware handshaking to determine when the other party (in this case the PDQ Board) is ready to accept data. The PDQ Board, however, does not implement hardware handshaking. In fact, a single driver chip on the UART Wildcard is used to implement both RS422 and RS485 communications for a given serial channel. You can implement the slave select lines by configuring Port A pins as outputs. This way, the lines will be biased to known voltages and nodes will not interpret the noise from undriven lines as actual data; without biasing resistors, the data lines float in such a way that electrical noise sensitivity is greatest when all device stations are silent or unpowered. Manufacturers are continuously improving the design and materials used in RS485 cables to ensure reliable and efficient data transmission in industrial environments. If your computer does not have an RS232 serial port, low cost USB-to-RS232 serial cables are available; contact Mosaic Industries for details. Please contact Mosaic Industries if you need this custom configuration. You will need to connect to a WiFi (home, work, laboratory, etc.) through which an MQTT Broker or the Internet is available. 2 wires is all you need to make it work.
Ideally, the two ends of the cable will have a termination resistor connected across the two wires. RS485 cable is a type of communication cable used in industrial applications to transmit data between devices over long distances. This page describes the serial ports and how to use them for instrument control and automation applications. These protocols are summarized on this page, but for more information regarding their data formats and their use for simplex or multi-drop serial lines, consult Understanding Serial Communications (but keep in mind that that page is directed to the use of the UART Wildcard, so it uses different driver functions). Rather, it relies on software handshaking via transmission of XON/XOFF characters (ascii 0x11 and 0x13, respectively) to coordinate data transfer and ensure that information is not lost when one of the communicating parties is busy. The data exchange format may be a line of ascii text. RS-485 is used for low-speed data communications in commercial aircraft cabins' vehicle bus. The WattNode® BACnet and Modbus® meters communicate using RS-485 (TIA/EIA-485-A) half-duplex, differential signaling at 9600, 19200, 38400, and 76,800 baud.
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. Once a character is sent the hardware reverts back into a receive mode in about 1-2 microseconds (at least with R.E. All of the RS232 signals start with the / (slash, pronounced not) character to indicate that the signals on the serial cable are logically inverted. The following table shows the connection diagram for a standard 9-pin serial cable. We can gain insight into the operation of the RS232 protocol by examining the signal connections used for the primary serial port in the above table. The following table summarizes the available serial channels. In other words, each local UART on the wildcard can both send data to and receive data from a remote UART on the other end of a connecting serial cable. Resistive termination - If the PDQ Board is at the end of the RS485 cable you can terminate the cable by installing jumper caps at both jumper locations, "Term" and "RTerm". The pinout of the PDQ Board’s Communications Header (H2), Docking Panel’s Communications Header (H1), and the Docking Panel’s Communications DB-9 Connectors are shown in the following tables.
These 9-pin standard DB-9 serial connectors are located on the back of the Docking Panel. Receiver Input Resistance (Ohms), (1 Standard Load for RS485) 3k to 7k 4k min. The RS422 driver and receiver use separate differential conductor pairs on the serial cables, enabling full duplex communications. SC, G or reference, the common signal reference ground used by the receiver to measure the A and B voltages. Category 5 (Cat 5, Cat 5e, and Cat 6) cables are the most common Ethernet cables in use today. RS232 is by far the most common serial protocol, and is the default protocol for both of the PDQ Board’s serial ports. The transmit and receive data signals carry the messages being communicated between the PDQ Board and the PC or terminal. RTU (Remote Terminal Unit) mode transmits 8-bit messages as two 4-bit hexadecimal characters in a continuous stream. To solve the "data collision" problem often present in multi-drop networks hardware units (converters, repeaters, micro-processor controls) can be constructed to remain in a receive mode until they are ready to transmit data. Two RS485 transceivers are present on the PDQ Board, one for each channel.