參數(shù)資料
型號(hào)： RS-422
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)： 36/44頁(yè)
文件大?。?/td> 628K
代理商： RS-422
RS-422/485 Application Note
33
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 434-7094
Chapter 5: Software
Introduction
RS-422 and RS-485 are hardware specifications. Software protocol is not
discussed in either specification. It is up to the system designer to define a
protocol suitable for their system. This chapter we will not attempt to define a
protocol standard, but will explain some of the issues that should be considered
by the system designer, whether writing or purchasing software.
RS-422 Systems
RS-422 system software differs little from the familiar point-to-point RS-
232 communication systems. RS-422 is often used to simply extend the
distance between nodes over the capabilities of RS-232. RS-422 can also be
used as the master node in a four wire master-slave network described later in
this chapter. When selecting or writing software for RS-422 systems the
designer should be aware of the signals being used by the hardware in the
system. Many RS-422 systems do not implement the hardware handshake lines
often found in RS-232 systems due to the cost of running additional conductors
over long distances.
RS-485 Driver Control
The principle difference between RS-422 and RS-485 is that the RS-485
driver can be put into a high impedance, tristate mode, which allows other
drivers to transmit over the same pair of wires. There are two methods of
tristating an RS-485 driver. The first method is to use a control line, often the
RTS handshake line, to enable and disable the driver. This requires that the
host software raise the RTS line before beginning a transmission to enable the
driver, then lower the RTS line after the completion of the transmission. Since
only a single RS-485 driver can be enabled on a network at one time it is
important that the driver is disabled as quickly as possible after transmission to
avoid two drivers trying to control the lines simultaneously, a condition called
line contention. Under some operating systems it can be difficult to lower RTS
in a timely manner and this method of driver control should be avoided
altogether.
The second method of RS-485 driver control we refer to as Automatic Send
Data Control. This type of control involves special circuitry that senses when
data is being transmitted and automatically enables the driver as well as
disabling the driver within one character length of the end of transmission.
This is the preferred method of driver control since it reduces software
overhead and the number of potential pitfalls for the programmer.
相關(guān)PDF資料
PDF描述
RS-485 RS-422 AND RS-485 APPLICATION NOTE
RS-MK-X2010 High Integrity FM Transceiver
RS3FS SDR Cable Assembly; Connector Type A:micro D Ribbon Plug; Connector Type B:micro D Ribbon Plug; Cable Length:2m; No. of Contacts:26; Pitch Spacing:0.8mm RoHS Compliant: Yes
RS3FS Damper Diodes (For TV)
RS4FS SDR Cable Assembly; Connector Type A:micro D Ribbon Plug; Connector Type B:micro D Ribbon Plug; Cable Length:5m; No. of Contacts:26; Pitch Spacing:0.8mm RoHS Compliant: Yes
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
RS422-GE1 制造商:Carlo Gavazzi 功能描述:CABLE FOR GE90
RS422-MI1 制造商:Carlo Gavazzi 功能描述:CABLE FOR MITS MASTER
RS422-MI2 制造商:Carlo Gavazzi 功能描述:CABLE FOR MITS MASTER
RS422-MI3 制造商:Carlo Gavazzi 功能描述:CABLE FOR MITS MASTER
RS422-OM2 制造商:Carlo Gavazzi 功能描述:CABLE FOR OMRON MASTER
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