Comtech EF Data HPOD - Basic Protocol

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HPOD C-, X-, Ku-Band High-Power Outdoor Amplifier Revision 6

Serial-Based Remote Product Management MN/HPOD.IOM

5–4

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

'Target'devicesareconnectedtothispair,andallsimultaneouslyreceivedatafromtheController.TheControlleristheonlydevicewith

aline‐driverconnectedtothispair–theTargetdevice

shaveonlyline‐receiversconnected.



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

connected.Allthe linedriversareheldinhigh‐impedancemode untilone(andonlyone) Targettransmi

tsbacktotheController.Each

Targethasauniqueaddress,andeachtimetheControllertransmits,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intended)willreply.TheTargete

nablesitsoutputlinedriverand

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



EIA‐485(fullduplex)summary:



• Twodifferentialpairs–onepairforController‐to‐Target,onepairforTarget‐to‐Controller.



• Controller‐to‐Targetpair hasonelinedriver(Controller),andallTargetshaveline‐receivers.



• Target‐to‐Controller pairhasonelinereceiver(Controller),andallTargetshaveTri‐Statedrivers.

5.3.2 EIA-232

This is a much simpler configuration in which the Controller device is connected directly to the Target via a two‐wire‐plus‐ground

connection.Controller‐to‐Targetdatais carriedviaEIA‐232electricallevelsononeconductor,andTarget‐to‐Controllerdataiscarriedin

theotherdirectionontheotherc

onductor.

5.3.3 Basic Protocol

WhetherinEIA‐232orEIA‐485mode,alldataistransmittedasasynchronousserialcharacters,suitablefortransmissionandre ception

bya UniversalAsynchronousReceiver/Transmitter(UART).Theasynchronouscharacterformatis8‐N‐1(8databits,noparity,1stopbit).

Thebaudratemayvaryfrom1200to1

9200baud.



Alldataistransmittedinframedpackets.TheController(assumedtobeaPCorASCIIdumbterminal)thatisinchargeoftheprocessof

monitor and control is the only device that is permitted to initiate, at will, the transmission of data. Targets are only  permitted to

transmitwhenth