SectionIII

3-96. DAV. After the talker placesdata on the data lines,it must set DAV LOW to indicatethat the datais vatid. A listener may not processdata until DAV goes LOW. DAV cannot be set HIGItr againuntil DAC goes HIGH, indicating that all listenershavefinishedproces- singthe data.

3-97. DAC. Whenall listenershaveaccepteddata,DAC goesHIGH, indicating to the talker that the data is no longer needed.A listenermay set RFD to HIGH at the same time or at any time after DAC goes LOW, to indicatethat it is readyfor new data.

3-98. Service Request, LSRO. Any unit on the bus having service request capability may set SRQ LOW at any time. This indicatesthat a unit wantsthe attention of the controller. The controller may then checkeach unit on the bus individually to seewhich unit or units pulled SRQ LOW, or it may ignore the servicerequest. LSRQ does not hinder other normal operationson the bus.

3-99. End Output, LEOP. Whenthe controller setsthe End Output line LOW, all units immediately stop driving DIOI - 8, MRE, DAV, RFD, and DAC. When EOp is HIGH, all units may operateaccordingto the normalbus rules.

3-100. Remote Enable, REN. All instruments on the bus are enabledto respondto remoteprogrammingdata if the controller holds the REN line LOW. The

Model3490A

listen addressof 6 and a talk addressof V. If two or more instrumentsare to be operatedon the samebus, they should not have the sameaddress.Table 3-6 lists the address codes possible. Address is selected by positioningjumper wires in a header on the Outgrrald Mother Board Assembly A3 1, shown in Figure 3-7. Removethe top coverto gainaccessto this header.Note that only five binary bits of the 7-bit format are selectable.These five bits are the same for both the listen and talk addressesThe. sixth and seventhbits are provided by the controller to determine whether the

addressis a talk or listen address;01for listen.l0 for talk. Absenceof a jumper is a logical"1";presenceof a

jumper is a logical"0". At leastonejumper must always be installed,becausethe 111I 1 addressis not allowed. This code is usedto unaddressthe instrumentto talk or listen.

.

-

a l

l r

 

- - ]

R 6

 

I u 4

I

- ^

a 3 l l

 

rÄi+: -cg-lL

 

-

R l z -

a e l i

l ^ ^ .

-

R r s -

- -

l i

F-

3490A may be set to remote operation by setting REN LOW and sendingits listenaddressIt. may be returnedto local

I

F <

J >

(front panel) control by settingREN HIGH. An exception is noted in Paragraph3-107. Normally, all units on the bus respond to their front panel controls when REN is HIGH.

3-101Talk.0nly(NoController).

3-102. The 3490A with the GPIB option may be used to provide data to a printer without havinga controller on the bus.The printer must be ableto acceptthe ASCII data information and to handshakewith the 3490A on the RFD, DAV, and DAC lines.The slide switchon the 3490^ rear panel must be set to the TALK ONLY position (see Figure 3-1). The instrument is then controlled by the front panel controls for selectionof function, range, Sample/Hold,and trigger mode. The 349OA may be triggered through the rear panel Trigger ConnectorJll, or allowedto sampleat a rate selected by the SAMPLE RATE control. Whena controller is connectedto the bus, the rearpanel switch must be set to the ADDRESSABLE position.

3-103GPIB.Controlof3490A.

3104. Listenand Talk AddressesThe. 34904 may be addressedto listenor to talk by settingMRE LOW and sendinethe properlisten or talk addressEach. 34904 GPIB I O is normally programmedat the factory for a

_r,ö

Figure3-7. Positionof JumperWireson Outguard MotherBoardAssemblyA31.

3-105. Addressedto Listen. When the 3490A is first turned on, the GPIB programmingcircuits will conform to the front panel control settings.It must be placedin remotecontrol beforeprogramming.

3-106. RemoteControl. To placethe 3490A in remote control, set MRE and REN to LOW and transmit the 3490A listen code. REN must be held LOW continuously to maintain remote control. When the instrument is first set to remote control, the GPIB circuitsstorethe front panel rangeand function selections.Sample/Hold mode is Off (S0), Triggeris set to Internal SampleRate (TQ), and Mode of Operationis AddressedMultiple with No Output (M0). AnV chalgesin this programmingmust then be made by remote control. LMRE must be set HIGH and the remote programmingdata transmitted. The 3490A will accept only the alpha identifiers E, F, M, R, S and T, and digits0 through 7. Table3-7 lists the 3490A programcodes.The 3490A may be unaddressed to listen by sendingthe character?. Figure 3-8 is a timing diagramfor data and handshakelines when the 3490A is addressedto listen.

3-107. Return to Local Control. The 3490A may be returned to local control by setting REN HIGH. How-