Rather, it relies on software handshaking via transmission of XON/XOFF characters to coordinate data transfer and ensure that information is not lost when one of the communicating parties is busy. A ground connection is also necessary to ensure that the communicating devices have a common voltage reference. Signal High and Lows are measured against the GND level so shifting the GND level will have a disastrous effect on the data transfer. There are a variety of ways the MOSI, MISO, SCK and /SS pins on your QScreen Controller can be connected. Many terminals and PCs, however, do rely on hardware handshaking to determine when the other party (in this case the QVGA Controller) is ready to accept data. While handshaking is still with us, it is usually best to disable it in software (if possible) and/or "loop-back" the pairs of signals (RTS to CTS, DTR to DSR, etc.) While RS232 was rumored to be on the "way out" with the advent of many of the new communications standards, it is still alive and well today. The byte-sized messages are transmitted and received via the MOSI (master out/slave in) and MISO (master in/slave out) pins. Converters between RS-485 and RS-232 are available to allow a personal computer to communicate with remote devices.



































Nowadays, we mostly use Wi-Fi for internet connectivity but earlier we used to use Ethernet cables going to each personal computer to connect it to the internet. The master computer broadcasts an address, a command code, a variable field and a checksum. The use of a checksum ensures that if data corruption does occur, the information is disregarded and the information is transmitted again. Shown below is the example of how a character is a transmitter over a UART data line. 2 Alphanumeric LCD, and MAX485 UART to RS485 converter IC connected to each end of an Ethernet Cat-6E cable via an RJ45 connector. In this case, cable connections may be made to Serial 1 on either the 10-pin Serial Communications Header or the Serial 1 Connector. Only one active master may control the network at a time; however, what is rs485 cable the device that assumes the role of master may change according to an appropriate protocol. A typical RS485 network can operate properly in the presence of reasonable ground differential voltages, withstand driver contentious situations, provide reliable communications in electrically noisy environments (good common mode rejection using twisted pair cable, shielding provides additional protection), and support thirty-two or more (many IC manufacturers have 1/2, 1/4, 1/8 unit load devices) drivers and receivers on the line.



































Up to 32-nodes (drivers and receivers) are allowed on one multi-drop, bi-directional network. 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. In general, all devices on a network should use the same phase, polarity, and baud rate clock signal. In fact, the program works the same as it did before, but now it is using the secondary serial port instead of the primary port -- and you didn’t even have to recompile the code! It works on half-duplex communication to implement the function of converting the TTL level into RS-485 level which means it can either transmit or receive at any time, not both, it can achieve a maximum transmission rate of 2.5Mbps. MAX485 transceiver draws a supply current of between 120μA and 500μA under the unloaded or fully loaded conditions when the driver is disabled. This works well and prevents the existence of ground loops, a common source of communication problems. On the other hand, RS485 is more industry-based communication which is developed for a network of multiple devices that can be used over long distances and at greater speeds too.



































Why is termination important in an RS485/RS422 network? Ideally, the two ends of the cable will have a termination resistor connected across the two wires and two powered resistors to bias the lines apart when the lines are not being driven. Twisted pair wire with a characteristic impedance of 120 ohms is recommended with 120 ohm termination at each end of the communications line. The RS485 receiver compares the voltage difference between both lines, instead of the absolute voltage level on a signal line. It operates on a differential signaling method of measurement rather than voltage measurement wrt GND pin. Initializing the 68HC11 as a slave (by clearing the MSTR bit in the SPCR control register as explained below) automatically configures the /SS pin as an input. When the 68HC11 controls the network, it is referred to as a "master"; otherwise, it is a "slave". For the transfer of data, the baud rates of both Master and Slave must be between 10% of each other. In this case, cable connections must be made to Serial 1 at pins 5 and 6 of the 10-pin Serial Header or pins 7 and 8 on the 24-pin Field Header.