參數(shù)資料
型號(hào)： RS-485
廠商： Electronic Theatre Controls, Inc.
英文描述： RS-422 AND RS-485 APPLICATION NOTE
中文描述： RS - 422和RS - 485接口應(yīng)用筆記
文件頁(yè)數(shù)： 37/44頁(yè)
文件大?。?/td> 628K
代理商： RS-485
34
RS-422/485 Application Note
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 434-7094
RS-485 Receiver Control
The RS-485 receiver also has an enable signal. Since RS-485 systems
using a two wire configuration connect the driver to receiver in a loopback
fashion, this feature is often used to disable the receiver during transmission to
prevent the echo of local data. Another approach is to leave the RS-485
receiver enabled and monitor the loopback data for errors which would indicate
that line contention has occurred. Although a good loopback signal does not
guaranty data integrity it does offer a degree of error detection.
Master-Slave Systems
A master-slave type system has one node that issues commands to each of
the “slave” nodes and processes responses. Slave nodes will not typically
transmit data without a request from the master node, and do not communicate
with each other. Each slave must have a unique address so that it can be
addressed independent of other nodes. These type systems can be configured as
two wire or four wire. Four wire systems often use an RS-422 master (the
driver is always enabled) and RS-485 slaves to reduce system complexity.
Four Wire Master-Slave Systems
This configuration reduces software complexity at the host since the driver
and receiver are always enabled, at the expense of installing two extra
conductors in the system. The Master node simply prefixes commands with the
appropriate address of the slave. There are no data echo or turn around delays
to consider. Since each of the slave transmitters share the same pair of wires,
care must be taken that the master never requests data from multiple nodes
simultaneously or data collisions will result.
Two Wire Master-Slave Systems
Two wire configurations add a small amount of complexity to the system.
The RS-485 driver must be tristated when not in use to allow other nodes to use
the shared pair of wires. The time delay between the end of a transmission and
the tristate condition becomes a very important parameter in this type system.
If a slave attempts to reply before the master has tristated the line, a collision
will occur and data will be lost. The system designer must know the response
time or turn around delay of each of the slave nodes and assure that the master
will tristate its driver within that amount of time. B&B Electronics’ Automatic
Send Data control circuits tristate the driver within one character length of the
end of a transmission.
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
RS485-232 制造商:PR 功能描述:
RS485-C1(AS) 制造商:未知廠家 制造商全稱(chēng):未知廠家 功能描述:RS232/RS485 CONV (AS)
RS485-C1(EU) 制造商:Equinox Technologies 功能描述:RS232/RS485 CONV (EU)
RS485-C1(UK) 制造商:Equinox Technologies 功能描述:RS232/RS485 CONV (UK)
RS485-C1(US) 制造商:Equinox Technologies 功能描述:RS232/RS485 CONV (US)
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