Comtech-ef-data PCB-4000 Manual do Utilizador descarregar pdf (Página 49)

5–1

Chapter 5. SERIAL REMOTE CONTROL

5.1 Overview

Remote monitor and control of the PCB‐4000 1+1 Phase Combiner is available either through an EIA‐485 multi‐drop bus (for the

controlofmanydevices)or an EIA‐232 connection(for the controlofasingledevice), anddataistransmittedinasynchronousserial

form using ASCII characters. Control and status inf

ormation is tr ansmitted in packets of variable length, in accordance with the

structureandprotocoldefinedinlatersections.

5.1.1 EIA-485

Forapplicationswheremultipledevicesaretobemonitoredandcontrolled,afull‐duplex(or4‐wireplusground)EIA‐485ispreferred.

Half‐duplex (2‐wire plus ground) EIA‐485 is possible, but is not preferred. In full‐duplex EIA‐485 communications, there are  two

separate,isolated,independent,differential ‐modetwistedpairs,eachhandli

ngserialdataindifferentdirections.



Itisassumedthata'Controller'device(aPCordumbterminal)transmitsdatainabroadcastmodeviaoneofthepairs.Many'Target'

devicesareconnectedtothispair,andallsimultaneouslyreceivedatafromtheController.TheControlleristheonlyde

vicewithaline‐

driverconnectedtothispair–theTargetdeviceshaveonlyline‐receiversconnected.



In the other direction, on the other  pair  each Target has a Tri‐Stateable line driver connected,  and the Controller has a line‐receiver

connected.Allthelinedriv ers areheldinhigh‐impe

dancemodeuntilone(andonlyone)TargettransmitsbacktotheController.Each

Target has a unique address, and each time the Controller trans mits, the address of the intended recipient Target is included in a

framed'packet'ofdata.AlloftheTargetsreceivethepacket,butonlyone(theintende

d)willreply.TheTargetenablesitsoutputline

driverandtransmitsitsreturndatapacketbacktotheControllerintheotherdirection,onthephysicallyseparatepair.

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