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Baud rates up to 56,000 baud are supported. Software-selectable baud rates up to 56,000 baud are supported. If it doesn’t, confirm that the terminal’s baud rate is correct by selecting the Comm item in the Settings menu of the Mosaic Terminal program, and click on 115200 baud. We assume that you are now communicating with the PDQ Board via the default Serial1 port at the standard 115200 baud rate. Port to modem communications usually use 300, 1200, 2400, 4800, 9600, 19200, 38400, 57600 and 115200 baud. Modem to modem lines often use 1200, 4800, 9600, 14400, 28800, 33600, and 56000 baud. Modem to phone line communications use rates of 110, 150, 300, 600, 1200, 2400, 3000, and 3200 baud. The primary and secondary serial communications ports are accessible through the QScreen's 10 pin, dual row Serial Header (H5) which is typically not installed, the 24 pin, dual row Field Header (H3), and through the individual DB-9 Serial 1 and Serial 2 connectors. A single master can broadcast commands to all the slaves, and can direct commands to an individual slave using its unique address. In the simplest scheme, all RS485 transceivers come up in receive mode when the interface is initialized, and each transceiver node has a unique address known to it and the master.

At any given time, rs485 cable only the master and a single active slave communicate. Remember that the /SS is active low so to select a device you need to set the pin low; otherwise the pin should idle high. In that case, when using very long cables you can improve noise immunity and assure a valid idle level when the transceiver is not active by installing bias resistors. Even though the MOSI pin is not connected to anything, the master initiates a transmission using a "dummy" byte. If you are using the QScreen as a master device, each external SPI device will require a separate select line (/SS). Move the serial cable from the "Serial Port 1" connector to the "Serial Port 2" connector on the QScreen. Because we chose the default baud rate (which the terminal is presumably already set for), you can simply move the serial cable from the Serial Port 1 connector to the Serial Port 2 connector on the Docking Panel to complete the change to the new port. When PE is set (equal to one), the most-significant bit in each byte transmitted will be a parity bit that is either set or cleared by the serial port automatically in order to achieve even or odd parity.

The remaining inactive slaves may actively receive, or listen to, data on the communications line, but only one slave at a time can transmit a message. The remaining "inactive" slaves may actively receive, or listen to, data on the communications line, but only one slave at a time can transmit a message. In these distributed processing networks, a variety of machines and instruments work locally, but communicate and share data or resources with one another globally using a single serial link. The Serial1 and Serial2 ports are is supported by the HCS12's dual on-chip hardware UARTs, and do not require interrupts to work properly. The PDQ Board's two serial ports support limited use of generating a parity bit. In summary, the code provided for implementing the second serial port is very flexible and can be used to support dual concurrent communications ports. Because all of the serial I/O routines on the PDQ Board are revectorable, it is very easy to change the serial port in use without modifying any high level code. If your application requires use of the secondary serial port as well as other interrupt routines, the key is to keep the interrupt service routines short and fast.

If your application requires RS485, use the primary serial port (serial1) for RS485 communications, and use the secondary serial port (Serial 2) to program and debug your application code using the RS232 protocol. We’ll use code from the GETSTART.c program which was introduced in the chapter titled Your First Program. Serial data is shifted out least-significant-bit first. The above parity settings will also determine how incoming data is interpreted (whether the most significant bit is considered a parity bit or part of the data being transmitted, and how many bits total to expect in each byte). An optional parity bit can be specified to enable error detection by the UART. So long as the error between the actual baud rate and that specified is less than 1.5% (or the error between transmitter and receiver is less than 3%) there should be no communication errors. The RS422 driver and receiver use separate differential conductor pairs on the serial cables, enabling full duplex communications. The RS232 driver and receiver use separate conductors on the serial cables, enabling full duplex communications. Each of the two UARTs on the wildcard is capable of full-duplex communications, meaning that both transmission and reception can occur simultaneously (although the RS485 protocol is half duplex as explained below).