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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. Thus in Table 9 6 , RTS1 is connected to CTS1, and DSR1 is connected to DTR1 and DCD1 onboard the QScreen Controller using zero ohm shorting resistors. 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. From the QScreen Controller’s point of view, these three signals (TxD, RxD, and ground) are the only connections required to perform serial communications. The cable shield must be earthed only in one point. 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. 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.

If you have already downloaded the program, you are ready to go. We found panels produced by JA Solar which are 1689 x 996mm and have a 330W output, and we could fit 5 or 6 of these on the roof between the chimneys. For example, at 4800 baud (bits per second), each bit lasts about 200 microseconds (µs), and if communications are full duplex (e.g., if the QScreen Controller echoes each incoming character), then there is a serial interrupt every 100 µs or so. We have built sophisticated instruments using the QScreen Controller that operate very reliably using multiple interrupts in addition to the software UART. Using the primary serial port is easy. 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. Our plans to upgrade our solar PV system this year are slowly progressing with installing a new Solis 1.5kW inverter and an EM112 Series Energy Meter, which have RS485 output and communicate using Modbus protocol. If you have not yet compiled the GETSTART program and you want to do the exercises here, open GETSTART.C in your TextPad editor, click on the Make Tool, and after the compilation is done, enter Mosaic Terminal by clicking on the terminal icon and use the "Send File" menu item to send GETSTART.DLF to the QScreen Controller.

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. Also, several non-serial interrupts can stack up; if they have higher priority than the serial interrupts, they will be serviced before the Serial2 interrupt routine, and again a serial input or output bit may be lost. These signals may alternatively be redirected to the digital inputs and outputs used by the second serial port if hardware handshaking is required. In this case, cable connections may be made to Serial 1 on either the 10-pin Serial Communications Header or the Serial 1 Connector. In this case, rs485 cable 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. Because the software UART is interrupt based, competing interrupts that prevent timely servicing of the Serial2 interrupts can cause communications errors on the secondary serial channel. 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.

We recommend that you keep the faster Serial1 port as the default serial link as you work through the exercises in this book. The secondary serial port is implemented by a software UART that controls two pins on PortA. On the other hand, the secondary serial port (Serial2) is implemented using hardware pins PA3 (input) and PA4 (output), and is controlled by the associated interrupts IC4/OC5 and OC4, respectively. In fact, you have been using it all along as you worked through the examples in this document. We also highly recommend using paired twisted cable for connecting most converters. By connecting pairs of these handshaking signals together, the terminal or PC can be made to think that the QScreen Controller is always ready to send and receive data. RX led. When connecting that RS485 adapter to the PC's COM port, sending data to that port would make the RX led flash. You might also consider operating the secondary serial port at a lower baud rate to relax the timing constraints.