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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. The QScreen Controller, however, does not implement hardware handshaking. There is no specific type of connector used to implement the RS485 protocol but in most scenarios, a DB9 connector or terminal block are employed. If you do this now, remember to move the QScreen Controller’s serial connector back to Serial Port 1, and to change the terminal’s baud rate back to 19200 baud using the "Comm" item under the terminal’s "Settings" menu. Move the serial cable from the "Serial Port 1" connector to the "Serial Port 2" connector on the QScreen. There are surface mount resistor pads on the QScreen that will allow you to bring out the secondary serial port to the Field Header on pins 5-6 or 7-8 as shown with the parentheses in Table 11-3. Pads are also available to bring out the RS485 signals to the DB9 Serial 1 Connector.

We can gain insight into the operation of the RS232 protocol by examining the signal connections used for the primary serial port in Table 9 6. The transmit and receive data signals carry the messages being communicated between the QScreen Controller and the PC or terminal. A jumper, J3, configures the primary serial port for either RS232 or rs485 cable (https://www.cap-rs485-imatek-chinh-hang.xyz) operation. Because all of the serial I/O routines on the QScreen Controller are revectorable, it is very easy to change the serial port in use without modifying any high level code. We’ll use code from the GETSTART.C program. The default serial routines used by the onboard kernel assume that full duplex communications are available, so you cannot use the RS485 protocol to program the controller. The RS485 connections are not brought out to the Serial 1 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. Although the RS232 protocol specifies functions for as many as 25 pins, each communications channel requires only three for simple serial interfaces: TxD1 (transmit data), RxD1 (receive data), and DGND (digital ground). Since both channels can operate simultaneously and independently, debugging can be performed while the application program is communicating via its primary channel.

The primary channel’s UART translates the bit-by-bit data on the serial cable into bytes of data that can be interpreted by the QED-Forth Kernel or by your application program. 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! Data translation between different machines can be performed with ease, and applications that communicate via the primary serial port can be debugged using the secondary channel. Serial 2 is implemented by a software UART in the controller’s QED-Forth Kernel that uses two of the processor’s PortA I/O pins to generate a serial communications channel. The SCK (serial clock) pin is a configurable synchronous data clock output. The communications is asynchronous because no synchronizing clock signal is transmitted along with the data. The CPHA bit determines whether data is valid on the leading or trailing edge of the clock.

It is designed to transmit data over long distances and in noisy environments. With noisy environments (our sites?) using the shield as ground is not always the most effective solution. 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. GT8E-3S-HU (Hirose) Connectors. CAN Communication between master and host. The Serial 1 port can be configured for either RS232 or RS485 communications at up to 19200 baud. If your computer does not have an RS-232 serial port, low cost USB-to-RS-232 serial cables are available; contact Mosaic Industries for details. Please contact Mosaic Industries if you need these custom configurations. While these signals provide a data path, they do not provide hardware handshaking that allows the two communicating parties to let each other know when they are ready to send or receive data. Many terminals and PCs, however, do rely on hardware handshaking to determine when the other party (in this case the QScreen Controller) is ready to accept data. In this manner, data can be exchanged between the master and each slave on the bus. You can use it to communicate with other devices.

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