Once the Data has been Exchanged > 자유게시판

Yes, it would work for that too, but 24 awg cable with plenum grade jacket is the standard. RS-485 standard conformant drivers provide a differential output of a minimum 1.5 V across a 54-Ω load, whereas standard conformant receivers detect a differential input down to 200 mV. This allows RS-485 to implement linear bus topologies using only two wires. With careful design, many peripherals can communicate via the SPI, and powerful multi-processor systems can be linked using this high speed bus. If the programmer has enabled the local interrupt mask for the SPI, an interrupt is recognized at this point. Any of these conditions may generate an interrupt if the SPIE (SPI interrupt enable) bit in the SPCR control register is set. The SPIE bit in the SPCR (SPI control register) enables SPI interrupt handling. If you are using the QScreen as a master device, each external SPI device will require a separate select line (/SS). RS-485, like RS-422, can be made full-duplex by using four wires.

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. It receives bytes sent by a slave device via the "master in/slave out" pin, MISO. This signal synchronizes the exchange of bytes between the QScreen and its peripherals. This ability to exchange messages means that the SPI is capable of full duplex communication. There are three flag bits implemented in the SPSR (SPI status register). There are a variety of ways the MOSI, MISO, SCK and /SS pins on your QScreen Controller can be connected. There are many possible configurations of master/slave networks. In some cases, however, a sophisticated network may have device groups on a network that use different clock configurations. The device that initiates a data transfer is the master, and all other devices on the network are slaves. Multiple receivers may be connected to such a network in a linear, multidrop bus. RS-485, also known as TIA-485(-A) or EIA-485, is a standard, originally introduced in 1983, defining the electrical characteristics of drivers and receivers for use in serial communications systems.

The flexibility and power of the 68HC11’s serial peripheral interface supports high speed communication between the 68HC11 and other synchronous serial devices. 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 detects the presence of more than one master on the SPI bus. Finally, for master devices, rs485 cable the SPR1 and SPR0 bits determine the baud rate at which data is exchanged. 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. It is important to note that when the CPHA bit is 0, the /SS line must be de-asserted and re-asserted between each successive data byte exchange (68HC11 Reference Manual, Section 8.3.2). If the CPHA bit is 1, the /SS line may be tied low between successive transfers.

To interface devices that support synchronized serial interfaces, but are not configurable like the QScreen, determine the device’s requirements for clock phase and polarity and configure the QScreen’s CPHA and CPOL accordingly. The clock’s polarity is controlled by a bit named CPOL (clock polarity) and its phase is controlled by CPHA (clock phase). If A is negative with respect to B, the state is binary 1. The reversed polarity (A positive with respect to B) is binary 0. The standard does not assign any logic function to the two states. RS-485 is used as the physical layer underlying many standard and proprietary automation protocols used to implement industrial control systems, including the most common versions of Modbus and Profibus. Digital communications networks implementing the standard can be used effectively over long distances and in electrically noisy environments. Care must be taken that an SC connection, especially over long cable runs, does not result in an attempt to connect disparate grounds together - it is wise to add some current limiting to the SC connection. This connection may be used to limit the common-mode signal that can be impressed on the receiver inputs. A ground connection is also necessary to ensure that the communicating devices have a common voltage reference.