Comtech EF Data HPOD - Basic Protocol

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.
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EIA‐485(fullduplex)summary:
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• Twodifferentialpairs–onepairforController‐to‐Target,onepairforTarget‐to‐Controller.
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• Controller‐to‐Targetpair hasonelinedriver(Controller),andallTargetshaveline‐receivers.
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• 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
eyhavebeenspecificallyinstructedtodosobytheController.
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