Se7en Worst Rs485 Cable Techniques > 자유게시판

For RS232 operation: Remove the jumper shunt from J3. For RS485 operation: Install the jumper shunt onto J3. A jumper, J3, configures the primary serial port for either RS232 or RS485 operation. 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! The master and slave could even exchange ascii QED-Forth commands. Even though the MOSI pin is not connected to anything, the master initiates a transmission using a "dummy" byte. 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. When it is low, the transceiver is in receive mode. QED-Forth includes three built-in routines to facilitate control of the RS485 transceiver. There are three flag bits implemented in the SPSR (SPI status register).

Our security solution products are based upon cutting edge technologies that are unique in the security industry. The CPHA bit determines whether data is valid on the leading or trailing edge of the clock. If the clock idles in the high state, the leading edge of the clock is a falling edge. Note that the data is changed by the transmitting device one half clock cycle before it is valid. Only one active master may control the network at a time; however, the device that assumes the role of master may change according to an appropriate protocol. 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). Likewise, the terminal’s transmit signal TxD is connected to the QScreen Controller’s receive signal RxD1. In this example, the QScreen Controller selects the serial A/D by outputting a LOW signal on /SS.

In general, all devices on a network should use the same phase, polarity, and baud rate clock signal. When the network master wants to talk to this particular slave, it outputs the slave’s ascii name onto the serial bus. After configuring the SPI system to communicate on a properly connected network of devices, sending and receiving data is as simple as writing and reading a register. If SPIF is set, reading the received data or initiating a new data transfer automatically clears the SPIF bit. Alternatively, the if the SPI interrupts are enabled, the SPI interrupt handler determines what caused the interrupt by reading the SPSR register to see which of the three status bits is set. Regardless of the network, however, there are only four signals used: SCK provides a synchronized clock, MOSI and MISO signals are used for data transmission and reception, and /SS configures the QScreen as a master or slave device. We have built sophisticated instruments using the QScreen Controller that operate very reliably using multiple interrupts in addition to the software UART. The QScreen Controller’s kernel software contains a complete set of high level driver routines for the Serial2 port, and these functions are summarized in the Control-C Glossary.

If you are running Serial2 at 4800 baud, the rest of your application must be able to function properly using the remaining portion of the CPU time. 1 running at the prior established baud rate (typically 19200 baud). The SPI can transfer data much more rapidly than an asynchronous serial link - its maximum rate is 2 Megabits/second. We recommend that you keep the faster Serial1 port as the default serial link as you work through the exercises in this book. By polling the Port A pin or by setting up an interrupt service routine, you can configure the QScreen to ignore the SCK input when /SS is high and keep MISO in a high-impedance state so that it does not interfere with the SPI bus. 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. It finds particular application in the Telecom and Industrial Diesel Generator where remote monitoring is employed. The Silence() routine searches the incoming serial characters for a pre-determined keyword (for example, the ascii "name" of this particular slave).

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