6 Strange Facts About Rs485 Cable > 자유게시판

UART is an Asynchronous transmission device hence there is no clock signal to sync the data between the two devices instead it uses start and stop bits at the start and end of each data packet respectively to mark the extremities of the data being transferred. An example of how a byte(0x3E) is transferred over the two lines of RS485 Communication. The PDQ Board's two serial ports support limited use of generating a parity bit. It is very well documented and widely used and it also has a parity bit to allow for error checking. This works well and prevents the existence of ground loops, a common source of communication problems. It works on half-duplex communication to implement the function of converting the TTL level into RS-485 level which means it can either transmit or receive at any time, not both, it can achieve a maximum transmission rate of 2.5Mbps. MAX485 transceiver draws a supply current of between 120μA and 500μA under the unloaded or fully loaded conditions when the driver is disabled. The QScreen Controller controls the RS485 transceiver with bit 5 of Port D of the processor.

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. This section describes the driver routines that control the RS485 transceiver, and presents some ideas that may prove useful in designing a multi-drop data exchange protocol. 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. We will send some data from the transmitter side over the cable from the Nano which is converted to RS485 signals via MAX RS485 Module working in Master Mode. Shield on communication cable is to remain continuous and ground only at the controller. 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. The receiver input has a fail-safe feature that guarantees logic high output if the input is open circuit. The RS232 signals are represented by voltage levels with respect to a system common (power / logic ground).

5V power supply and the rated current is 300 μA. But if you are building a control system with these development boards over a distance greater than 10 to 15 meters, then you should take the noise and signal power into consideration because if you want your system to work reliably, then you cannot afford to lose the data while transferring. We have been using Microcontroller Development Boards like Arduino, Raspberry Pi, NodeMCU, ESP8266, MSP430, etc. for a long time now in our small projects where most of the times distance between the sensors and board is not more than few centimeters at max and at these distances, the communication between the different sensor modules, relays, actuators, and controllers can be easily done over simple jumper wires without us being worried about the signal distortion in the medium and the Electrical noises creeping into it. The main reason behind using these Ethernet Cables over normal wires is that they provide much better protection against noise creeping in and distortion of the signal over high distances.

Sig- lines are twisted as twisting nullify the effect of electromagnetic noise induced in a cable and provide a much better immunity against the noise which allows the RS485 to transmit the data up to 1200m of range. They have Shielding Jacket over the insulation layer to protect against the Electromagnetic Interference and also each pair of wires is twisted together to prevent any current loop formation and thus much better protection against the noise. On the other hand, RS485 is more industry-based communication which is developed for a network of multiple devices that can be used over long distances and at greater speeds too. To ensure that no two devices drive the network at the same time, it is necessary that each slave device be able to disable its own RS485 data transmitter. In general, all devices on a network should use the same phase, polarity, and baud rate clock signal. Bias termination - Using resistive termination decreases noise immunity, particularly if the cable is loaded with many devices.

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