• 목록
• 답변
• 글쓰기
• 게시판 리스트 옵션
  • 수정
  • 삭제

The master initiates a communications request to a "slave node" by addressing that unit. RTS (Request to send) does have some utility in certain applications. Differential data transmission (balanced differential signal) offers superior performance in most applications. RS422. RS422 is also specified for multi-drop (party-line) applications where only one driver is connected to, and transmits on, a "bus" of up to 10 receivers. Below you will see a cabling example for one master and two slaves in a full-duplex and a half-duplex situation. Independent channels are established for two-way (full-duplex) communications. The wires are named A (negative) and B (positive). The recommended arrangement of the wires is as a connected series of point-to-point nodes, a line or bus. RS485 meets the requirements for a truly multi-point communications network, and the standard specifies up to 32 drivers and 32 receivers on a single (2-wire) bus. The connection between two or more elements (drivers and receivers) should be considered a transmission line if the rise and/or fall time is less than half the time for the signal to travel from the transmitter to the receiver.

The hardware detects the start-bit of the transmission and automatically enables (on the fly) the RS485 transmitter. The specification allows for data transmission from one transmitter to one receiver at relatively slow data rates (up to 20K bits/second) and short distances (up to 50Ft. @ the maximum data rate). Only one driver may be in the on at the time. Read rates vary with counters, since they are normally controlled by the user entry Gate Time. While the standards bring uniformity to data communications, many areas are not specifically covered and remain as "gray areas" for the user to discover (usually during installation) on his own. To solve the "data collision" problem often present in multi-drop networks hardware units (converters, repeaters, micro-processor controls) can be constructed to remain in a receive mode until they are ready to transmit data. Once a character is sent the hardware reverts back into a receive mode in about 1-2 microseconds (at least with R.E.

In its simplest form, a pair of converters from RS232 to RS422 (and back again) can be used to form an "RS232 extension cord." Data rates of up to 100K bits / second and distances up to 4000 Ft. To get the solar PV power from the roof down to the basement shed, we purchased 20 meters of 6mm armoured cable; this was routed down the back of the house and into the shed through the stone wall. RS485 extends the common mode range for both drivers and receivers in the "tri-state" mode and with power off. Also, RS485 drivers are able to withstand "data collisions" (bus contention) problems and bus fault conditions. Is there an easy way to log data to a PC from multiple instruments on an RS485 bus? Henceforth, we shall consider Slave devices to be measuring instruments with serial communication, even if the cabling is similar for all Modbus devices. If the PC is connected to the multiple Laureate instruments on an RS485 bus via an Ethernet-to-RS-485 gateway board or a USB-to-RS485 gateway board, use Laurel’s free XLOG2 datalogging software. Systems of this type (4-wire, half-duplex) are often constructed to avoid "data collision" (bus contention) problems on a multi-drop network (more about solving this problem on a two-wire network in a moment).

With the introduction of "automatic" repeaters and high-impedance drivers / receivers this "limitation" can be extended to hundreds (or even thousands) of nodes on a network. A true multi-point network consists of multiple drivers and receivers connected on a single bus, where any node can transmit or receive data. Differential signals can help nullify the effects of ground shifts and induced noise signals that can appear as common mode voltages on a network. The RS232 signals are represented by voltage levels with respect to a system common (power / logic ground). We found that there are 10K ohm resistors fitted on the A & B data lines with the A channel having a 10K pull-up resistor to 3.3 volts and the B channel having a 10K pull-down resistor to ground. Ideally, the two ends of the cable will have a termination resistor connected across the two wires and two powered resistors to bias the lines apart when the lines are not being driven. The shielding may be braided (be formed by a mesh of thin conducting wires) or be a foil (consisting of a sheet of metal wound around the conductors): the two types are equivalent.

Should you loved this article and you would want to receive details concerning rs485 cable please visit the site.