Understanding RS485 Standard and Working of RS485 Transceiver - Embedded Hardware Design > 자유게시판

The maximum data transfer rate of RS485 is 10 Mbps over a distance of up to 1200 meters. Due to this and it being able to transmit data over long distances, the RS485 is used commonly as a protocol for POS, industrial and telecom. The maximum recommended distance was 1.2km or 4000 feet and the data rate was limited to 100kbps. Over the years, the standard and its data transmission speed have evolved for the better. The maximum slew rate also limits the maximum communication speed on the line. The transmission speed possible with an RS232 interface is 1Mb/s for a distance of up to 15 meters. On the other hand, RS-422 commonly supports full-duplex operation, allowing for simultaneous transmission and reception of data. For example; EIA-449 and EIA-530 are connector standards that reference RS-422 for electrical levels. RS-422 allows for multiple receivers on each pair, but only one driver. So it does not matter where the driver is connected on the cable, it "sees" a 60 Ω load. Unit Load: The network’s unit load impacts the number of devices that can be attached to it. Multipoint operation from a single 5-V or 3.3V supply: RS-485 allows multiple devices (up to 32 unit loads) to be connected to the same communication bus, powered by a single 5-volt or 3.3-volt power supply.

Drive Capacity: The drive capacity of EIA-485 is 32 unit loads, which means 32 units of 12kΩ receivers are connected parallelly. One method involves selecting receivers with built-in fail-safe input thresholds. Also note that the symbol does not show the input. Note that the RS-422/485 standards call for "balanced interconnecting media", not twisted pair. The following table provides an overview of the two standards. The Electronics Industry Association (EIA) has produced standards for RS485, RS422, RS232, and RS423 that deal with data communications. Making effective use of serial devices often involves converting between RS232, RS485, and USB signals. However, Arduino and Raspberry Pi hobbyists also use it for some of their projects when multiple peripherals need to be linked to the board. However, a drawback is that every node on the network must feature this built-in capability. However, in a full-duplex setup, they are limited to a master and slave communication where slaves cannot communicate with each other.

This particular implementation of two RS-485 networks is often called 4-wire or full-duplex RS-485. RS-232 only defines connecting DTE to DCE, so when two computers are connected together this is outside of the standard. Many think the RS-232 standard completely defines the IBM PC serial port, but this is incorrect. RS-232 provides a list of circuits and says if you use a circuit; this is what it must do and it must be on this pin of the connector. RS-232 is only defined for point-to-point connections, so you need a separate cable for each sensor connected to a host CPU. Der SRF485 Sensor verwendet den RS485-Standard für die Kommunikation mit bis zu 127 Modulen. Die Reichweite des SRF485 beträgt 30 cm bis 5 Meter. This article aims to explore this topic and assist you in selecting the flow meter that best suits your needs. Maximum Cable Length 50 FT. Low capacitance cable becomes important when pushing line length and/or data rates to the maximum. It supports maximum data rates at a length of 1200 meters, making the RS485 protocol an excellent choice for communication between physically distant pieces of equipment.

The RS485 protocol employs a differential voltage system that allows it to operate effectively in environments with higher levels of electrical noise. This allows for the creation of multipoint networks where several devices can communicate over the same twisted-pair cable. If multiple devices start to talk at the same time, the data may be corrupted. A byproduct of the differential voltage system is the extended data transfer distance, increased transmission speed, and lower voltage use seen with RS485. Another approach is to use additional external resistors to establish an external bias on the idle bus. Although this voltage may be insufficient to switch the receiver state directly, an internal bias current within the attenuation network creates a voltage difference at the receiver comparator input. These high voltages need attenuation down to voltages that 3.3 V or 5 V transceivers can handle. A typical attenuation factor should be on the order of 10 to 1, effectively reducing the magnitude of the voltages present internally at the comparator. R4 and R6 are connected to the negative input terminal of the comparator.

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