Slacker’s Guide To Rs485 Cable > 고객센터

The secondary serial port is connected similarly except that the onboard connection of /RTS to /CTS, and /DSR to /DTR are permanent. We assume that you are now communicating with the PDQ Board via the default Serial1 port at the standard 115200 baud rate. 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. Note that the local and the remote must share a common ground, so a minimum of 3 wires are required for full duplex RS232 communications: a transmit wire, a receive wire, and a common ground. Newer protocols include the full duplex RS422 and the half duplex RS485 protocols, each of which drives differential 0 to 5 volt signals on the serial cable. The value of each termination resistor should be equal to the cable characteristic impedance (typically, 120 ohms for twisted pairs). They should generally not be needed, except if you use long cables, multiple RS485 devices, and resistive termination. RS485 avoids this issue which also allows for shielding of the cables to prevent noise. This allows for basic error detection, in that if noise on the transmission line causes one bit to be received incorrectly, either received as a '0' when transmitted as a '1' or vice-versa, the error would be detected due to the count of '1' bits in the byte being odd when it is expected to be even, or vice-versa depending on the parity checking settings.

In either of these cases, a source of noise that caused one bit to be received incorrectly would invalidate the received byte, since the total number of '1' bits would be odd rather than even. This is an extra single bit appended to the end of each byte or character transmitted, which is set or cleared as necessary to ensure that the total number of '1' bits in the byte is always odd or even. 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. 1 running at the prior established baud rate (typically 115200 baud). When the keyword name is received by the Silence() routine running in the slave, the slave PDQ Board executes RS485Transmit() to send an acknowledgment to the master (which should now be listening to the serial bus to accept the acknowledgment). Resistive termination - If the PDQ Board is at the end of the RS485 cable you can terminate the cable by installing jumper caps at both jumper locations, "Term" and "RTerm". RC termination - In some applications requiring low power you may not want to load the line with 120 Ω resistors at each end.

Circuits may be terminated on screw terminals, D-subminiature connectors, or other types of connectors. In this case, cable connections may be made to Serial 2 at pins 4 and 10 of the PDQ Board’s 10-pin Serial Header, or pins 5 and 6 of the Docking Panel’s 10-pin right-angle Serial Header. By default, the RS485 connections are not brought out to the Docking Panel’s DB-9 Serial1 Connector. By default, the RS485 connections are not brought out to the Docking Panel’s DB-9 Serial1 Connector, although custom placement of zero-ohm surface-mount resistors on the Docking Panel can route the RS485 signals to the DB-9. In this case, cable connections may be made to Serial 1 on either the 10-pin PDQ Board Serial Communications Header, or the Docking Panel’s 10-pin right-angle Serial Header, or the Docking Panel’s Serial1 DB-9 Connector. From the PDQ Board’s point of view, these three signals (/TxD, /RxD, and ground) are the only connections required to perform serial communications. The arrows in the diagram point to pins configured as inputs, and originate from output pins. The serial output at the UART idles at the logic high (mark) level. However this contradicts the facts that an idle mark state is a logical one and the termination polarization puts B at a higher voltage in Profibus guidelines.

Bias termination - Using resistive termination decreases noise immunity, particularly if the cable is loaded with many devices. No termination - If the PDQ Board is not an end device, you should not terminate that cable. The other end of the cable should be terminated similarly. The end devices are responsible for terminating the cable so that there are no reflections from the cable ends. Therefore for RS485 communications no crossover cable is used. That places a 120 Ω resistor across the RS485 differential line at the driver chip. In that case you may terminate the lines with a series RC network comprising a 0.1 μF capacitor in series with a 120 Ω resistor. HD-SDI series delivers crystal clear mega pixel images without compression over coax. Rs485 is low impedance balanced , so twisting the pair helps with noise immunity as well as reducing the attenuation effect of higher baud rates due to the parallel capacitance of the wires in the cable jacket over the long lengths. You aren’t limited to fifty feet of cable like with RS232. If your application requires RS485, you can use the secondary serial port (serial2) to program and debug your application code using the RS232 protocol, and use the primary serial port (Serial1) for RS485 communications.