Right here Is a technique That Helps What Is Rs485 Cable > 자유게시판

Function prototypes for this function and other versatile serial I/O routines are defined in the COMM.H header file, and are described in detail in the Control-C Glossary. 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 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! Once you have selected the appropriate firmware, select the "??(O)" button. These detailed signal descriptions and cable diagrams are presented to provide complete information for those who have special communications requirements and for those who wish to make their own application-specific communications cables. Given the availability of ready-made communications cables, what is rs485 cable it is not necessary to study or understand the following descriptions of cable connections. The RS485 connections are not brought out to the Serial 1 Connector. The byte-sized messages are transmitted and received via the MOSI (master out/slave in) and MISO (master in/slave out) pins. This ability to exchange messages means that the SPI is capable of full duplex communication. The master and slave could even exchange ascii QED-Forth commands.

The only difference between the master and slave devices is that the master initiates the transmission. 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. Although the devices would share the same network, communications would only be understandable by members of the same group. 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 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. The QED-Forth kernel includes pre-coded drivers that configure and control the SPI for maximum speed data transfers.

The two lowest order bits in the SPCR control register, named SPR1 and SPR0, determine the data exchange frequency expressed in bits per second; this frequency is also known as the baud rate. To further reduce the effects of interference, a low Baud rate of 2400 (or 1200) Baud is used. 1200 is the baud rate that you choose; you can specify any standard baud rate up to 4800 baud. Thus, as a rough approximation, operating at 4800 baud full duplex requires about 40 to 50% of the 6811's CPU time (that is, an average of approximately 40 to 50 µs service time every 100 µs). Moreover, if Serial2 is running full duplex at 4800 baud, any other interrupt service routine that takes longer than 100 µs is likely to cause a problem. The Silence() routine searches the incoming serial characters for a pre-determined keyword (for example, the ascii "name" of this particular slave).

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 Serial2 channel is always configured for RS232 communications, and can sustain baud rates up to 4800 baud. The Serial 1 port can be configured for either RS232 or RS485 communications at up to 19200 baud. The RS485 protocol uses differential data signals for improved noise immunity; thus RS485 can communicate over greater distances than RS232. Thus RS485 is the standard protocol of choice when multi-drop communications are required. Table 9-6 shows the connection diagram for a standard 9-pin serial cable. 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 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.