Bronkhorst RS232 interface Manual de usuario descargar pdf (Pagina 10)

BRONKHORST®

Page10RS232interface    9.17.027

3 FLOW‐BUSPROTOCOLDESCRIPTION

3.1 GENERAL



Onthe highest supported communication level, you may use DDE‐channels for Windows application‐programs with

thisfacility.Onalowercommunicationlevel,youcanusetheFLOWB32.DLL,forchangingparametervalues.



ToreadandwriteparametervaluesfromortoFLOW‐BUSdevicesdirectlythroughtheavailableinterfacesthere

isa

special protocol for messages between these devices. When operating a FLOW‐BUS system with a HOST computer,

youneedtoknowthismessageprotocolifyouchoosetodrivetheinterfacesdirectly.



When you use a type of RS232/FLOW‐BUS interface (baud rate up to 38K4) you may

 first have to initialise the

interface.ThiscanbedonebymeansofsendingsomeASCII‐stringstotheinterfacethroughRS232.

Seealsoparagraph“InitialisingRS232/FLOW‐BUSinterface”



TherearetwodifferentcommunicationprotocolsforthePCandtheRS232HOST:



 anASCIIprotocolforcommunicationthatiscompatiblewithexistingFLOW‐BUSapplications.

Thisprotocolservesonlyonemaster/slavedialogatatime.



 anenhancedbinaryprotocolthatsupportsconcurrentsendingofmessagestodifferentnodes.Thisprotocol

containsamessage‐sequencenumberandservesmorethanonemaster/slavedialogsatatime.



TheRS232‐HOSTmoduleautomaticallyrecognisestheprotocolusedbythePCandadaptsitsbehaviourtothe

protocolin

use.Thetypeofprotocolisdeterminedbythefirstcharacterofamessage.



 Thefirstcharacteris‘:’ (0x3A) existingtypeofmessage.

 ThefirstcharacterisDLE (0x10) enhancedtypeofmessage.



ViatheFLOW‐BUSDLL(FLOWB32.DLL)thePCdetermineswhichprotocolisinuse.



Thecommunicationrelationisalwaysmaster(PC)andslave(HOST).TheHOSTwillalwaysrespondonarequestfrom

thePC.



3.2 INITIALISATIONOFLOCALHOSTINTERFACESONMULTIBUSINSTRUMENTS



WhenyouuseadigitalinstrumentwithRS232interface,baudrateisfixedon38K4baudandnospecialinitialisationis

needed.ThroughtheseriallineconnectedtoaCOM‐portofyourcomputerortoaPLCyouhavetocommunicatewith

theinstrumentusingtheFLOW‐BUSprotocol.

Eachinstrumenthasitsownnodeaddress(3...120).Ifyouwanttosend

amessage totheinstrumentyouhave toknowthisnodeaddress. However,if yousend a messagetonode address

128theinstrument willalwaysrespondto your message.On a  point‐to‐pointconnection likeRS232

it is  theeasiest

way to make the communication work under all circumstances (it is independent of the real node address of the

instrument).

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