Since Pi's built-in UARTs don't support the RS485 standard, rs485 cable I'm using the USB-RS485-WE-1800-BT FTDI cable. The processor chip in this converter cable is the high performance FTDI chip which is compatible with all versions of Windows (32- and 64-bit), Mac and Linux. The terminal’s serial receiver chip re-inverts the signal to its positive sense. The following table shows the connection diagram for a standard 9-pin serial cable. Designed with industry standards, it comes with a waterproof aviation connector to ensure that your connection will not be affected by the elements. The RS485 (EIA485) interface has proved to be extremely robust and is the most popular communication protocol used in industry due to its multi-point topology. The RS422 protocol has similarities with RS485 in that both conduct data transmission using differential signals. These pins are normally used for the DTR, data terminal ready and DSR, data set ready signals. You can implement the slave select lines by configuring Port A pins as outputs.

The Silence() routine searches the incoming serial characters for a pre-determined keyword (for example, the ascii name of this particular slave). It is not a standard Communication protocol, but it is a physical circuit with which you can transmit and receive serial data with other peripherals. Most computers conform to IBM PC AT-compatible RS232 interfaces which use 9-pin D-Type connectors, consequently the QScreen Controller brings out its serial ports to two female 9-pin D-Type connectors. However, most RS232 ports have been replaced in personal computers by USB today. Newer equipment uses a USB interface more commonly. Writes characters to the RS485 interface. Sets the configuration for the RS485 Modbus communication. Slave Address: Address to be used as the Modbus slave address in Modbus slave mode. For the transfer of data, the baud rates of both Master and Slave must be between 10% of each other. Multi-drop configurations enable up to 32 devices to be connected with a single controlling master device. Connect RS485 devices with 2 contacts. RS485 in full duplex mode 4 contacts are employed. Connect RS485 devices with 4 contacts. For the QScreen, /SS is not used for SPI communication because it is used to control the direction of the RS485 transceiver; you can use any digital I/O line as a /SS signal.

Automatic send data control is enabled by default so no external flow or handshake control is needed. The cable itself is powered from the USB port so no additional external power supply is needed for this RS 485 converter to work. Compact USB to RS-485 converter cable with the chipset built into the USB connector. This USB to 485 converter is surge and static protected to protect against the most common damages from static electricity and other voltage spikes, which makes it suitable for most applications, including industrial, commercial and any general office environment. It operates on a differential signaling method of measurement rather than voltage measurement wrt GND pin. Sets the mode of the Bricklet in which it operates. Sets the configuration for the RS485 communication. By default the LED shows RS485 communication traffic by flickering. If you call this function with the SHOW ERROR option again, the LED will turn off until the next error occurs. In Modbus slave mode this function can be used to answer a master request to read coils. Master Request Timeout: Specifies how long the master should wait for a response from a slave when in Modbus master mode.

If the /SS pin of the master is an input and if a low input level is detected, the processor sets the MODF bit in the SPI status register a "mode fault" condition. If PT is cleared, then all transmitted bytes with a parity bit will have an even number of total '1' bits. In either of these cases, a source of noise that caused one bit to be received incorrectly would invalidate the received byte, since the total number of '1' bits would be odd rather than even. You will find the source code for the Thermostat on our website. You will be able to determine the actual configuration based on the documentation that accompanied the device. Returns the configuration as set by SetRS485Configuration(). See SetRS485Configuration() for configuration possibilities regarding baudrate, parity and so on. By default the error LED turns on if there is any error (see ErrorCountCallback callback). If the Bricklet is in bootloader mode, the LED is off.