4 Issues I would Do If I would Start Again RS485 Standard > 자유게시판

Digital logic usually uses the same convention (but not the same voltage) as the lamp example. At the other end of the cable is (typically) the same thing -- the connectors, the RS-485 interface IC, and a UART inside a microcontroller. Even though the logic function of the generator and receiver are not defined by RS-485, it makes sense to many engineers to have a binary 1 appear on the RS-485 wires when a binary 1 is being transmitted. Before we discuss polarity lets take a look at logic levels and binary states. Environments that exhibit high levels of electrical noise and variable ground potential impact RS232’s ability to transfer data efficiently and can lead to data loss or corruption. A long 3-conductor cable intended for RS-232 can often be switched to half-duplex RS-485, allowing communication at higher speeds and at higher external noise levels than the same cable used with RS-232 signaling. Many other IC manufacturers make a drop-in replacement for this IC, and many of them (such as the MAX483) use the same labeling. We repeat, all versions can be configured to transmit to a script on a Web server - it can be your "real" web server or a virtual web server of a home automation system (eg ControlHUB), automation home assistant; and they can use MQTT.

RS-422 is full duplex so it can use the X-On / X-Off protocol, if needed. Although many applications use RS-485 signal levels, the speed, format, and protocol of the data transmission are not specified by RS-485. ↑ "RS-422 And RS-485 Applications Ebook" (PDF). RS-422 is similar (except they leave the hyphen out) Both standards have a section defining why you may want fail-safe operation, but neither discuss how to implement it. The signal will eventually stabilize (until the next bit transition) so the slower the bit rate the more time the signal will have to stabilize before it is sampled (usually by a UART). This applies to the 8 bit version of the original 50 way SCSI interface. Well if you paid attention to the previous discussion, there is no way. 2) the GSM version also allows you to indicate a possible PIN (leave blank if there is no PIN) and the manager's APN (search for it on Google if you don't know). So how do you know what pin is "A" and what is "B"? While it may seem quite rational to assume that an RS-485 driver IC pin that is labeled A matches the RS-485 standard's wire "A", this is actually an assumption and is in fact not the case.

Fail-safe is mentioned twice in RS-485. As mentioned above in the Voltages section; On the RS-485 network there will be times when the two wires are not driven by a transmitter. There is no way to say that a termination resistor will always increase the line length the network. A 120 Ω resistor on a 100 Ω cable will dramatically reduce the ringing compared to no termination. The ringing will also stabilize faster in shorter cables. Branching the cable to a receiver will cause secondary reflections which will cause more and unpredictable ringing of the signal. This will cause reflections both back to the driver and forward to other receivers on the cable. RS-485 typically uses a linear network with bidirectional signal wires: There are typically many devices along a RS-485 shared cable. But this is only true if there is no ringing or noise on the line that switches the receiver back to a 0 at the end of the stop bit. For those designing or documenting a system, it is a bit more complicated than simply swapping pins. Don't assume that the A and B pins of an IC match the "A" and "B" of the RS-485 standard because they can't.

The entire subject of handshaking is obsolete with modern USB to RS-485 adapters since the PC's driver's and/or hardware handle driver enabling, RS485 standard and a modern PC can handle data rates much faster than can be transmitted over an RS-485 network. The RS485 and RS232 serial communication protocols have been in use for over 50 years and are still widely used throughout business and industry. A byproduct of the differential voltage system is the extended data transfer distance, increased transmission speed, and lower voltage use seen with RS485. In a RS-485 cable, data typically flows in both directions along any particular wire, sometimes from the "A" of the first device to the "A" of the second device, and at a later time from the "A" of the second device to the "A" of the first device. Since a receiver may have a loading of less than one, the actual number of receivers that can be connected depend on the unit load rating of the receivers, as well as the wire, bit rate, stub lengths, biasing and termination of the network. If the data bit is sampled while there is ringing it may be sampled as an incorrect value. Finally there is confusion from the IC manufacturers.