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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. 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. To use a QScreen as a slave in a multi-drop network, simply define a word, (named Silence(void), for example) that when executed calls RS485Receive() to wait for any pending character transmission to complete, then disable the transmitter, and then execute a routine such as Key() to listen to the communications on the serial bus. In the most common multi-drop RS-485 protocol, one computer is designated as a "master" and the rest of the computers or devices on the serial bus are designated as "slaves". In theatre and performance venues, RS-485 networks are used to control lighting and other systems using the DMX512 protocol. 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.

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 primary serial channel can operate at standard speeds up to 19200 baud and can be configured for either RS232 (the default) or RS485 operation. The flexibility and power of the 68HC11’s serial peripheral interface supports high speed communication between the 68HC11 and other synchronous serial devices. The QED-Forth kernel includes pre-coded drivers that configure and control the SPI for maximum speed data transfers. With careful design, many peripherals can communicate via the SPI, what is rs485 cable and powerful multi-processor systems can be linked using this high speed bus. What made it such an advancement over RS232 was the fact that it could transmit not only a single device to device transmission, but also a communications bus to connect multiple devices at once. The Serial2 channel is always configured for RS232 communications, and can sustain baud rates up to 4800 baud.

For RS232 operation: Remove the jumper shunt from J3. In this section we will consider the most general and simple configurations. Thus, resetting the SPIF flag is very simple. Thus, the master has only one input, MISO, which is the slave’s only output. There are a variety of ways the MOSI, MISO, SCK and /SS pins on your QScreen Controller can be connected. Slave devices use the master in/slave out pin, MISO, for transmitting, and the master out/slave in pin, MOSI, for receiving data. The byte-sized messages are transmitted and received via the MOSI (master out/slave in) and MISO (master in/slave out) pins. It receives bytes sent by a slave device via the "master in/slave out" pin, MISO. As the master transmits its data, 8 bits of data are simultaneously received. Consult the data sheets for any peripheral devices that you are interfacing to the SPI and, if a different configuration is needed, follow the instructions below to set up the appropriate SPI data transfer protocol. This chapter describes those drivers, and presents code that makes it easy to configure the SPI for different data transfer rates and formats. If you are using the QScreen as a slave device and require the /SS signal for your external SPI hardware, configure one of the Port A pins on the Field Header as an input pin.

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. Table 9-6 Serial Cable Connections. When the network master wants to talk to this particular slave, it outputs the slave’s ascii name onto the serial bus. When the keyword name is received by the Silence() routine running in the slave, the slave QScreen Controller executes RS485Transmit() to send an acknowledgment to the master (which should now be listening to the serial bus to accept the acknowledgment). The Serial Peripheral Interface, SPI, is a fast synchronous serial interface. The SCK pin’s synchronous clock signal has configurable phase, polarity and baud rate so that it can interface to a variety of synchronous serial devices. 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.