Model 34904

either HIGH or LOW, the output is LOW. The HIGH/ LOW switch on the Outguard Data Output Assembly controls one input to each gate. When the HIGH/LOW switch is set to HIGH, one input to each gate is always LOW; consequently, the output will be the samelogic level as the other input. When the switch is set to LOW, one gate input is always HIGH. Consequently, if the other input is alsoHIGH, the output will be LOW, and if the input is LOW, the output will be HIGH.

4170. DataFlag.

+171. The Data Flag output signalgoesHIGH at the begiruring of a measurementand LOW after a reading sequenceis completed. The HIGH to LOW transition indicates that the Data Output information is ready. This transition constitutes a Print Command to a digital recorder. If the instrument is operatingin the autorange mode, Data Flag remains HIGH until a reading on the correct rangehasbeencompleted.

L172. kinter Hold.

+173. A HIGH signalfrom a digitalrecorder,indicating that the recorder is not ready for an input, is inverted and connected to the 349OA Hold line. This prevents automatic samplinguntil the Printer Hold signalreturns

to LOW. A slide switch on the Outguard Data Output printed circuit board permits disabling of the printer

Hold line. If the switch is in the IN position and the

Printer Hold line is left open, the inverting transistor output may go LOW, resultingin a ..Hold" condition.

4t74.REM0TEC0NTR0t0PTtoN022.

+175. The Remote Control Option permits remote control of range, function, autorange selection, and Sample/Hold operation. All connections at the rear panel Remote Input connector are isolated from the 34g0{internal circuits. Power to the outguard circuits is supplied by the + 5 V outguard power supply. Outguard ,r-. ground is isolated from inguard circuit common and from chassis(earth) ground, and may be floated up to

40 V above chassis. Figure 7-33 is a diagram of the Remote Control circuits.

l}176.Gircuitlsolation.

1.177. A photo-isolator,consistingof a light-emitting diode which drives a photosensitivJtransistoi, is usedto

carry eachsignalacrossguard.Consequently,thereis no electrical connection bätween inguärd and outguard circuits.

4-178.RemoreEnable.

4-179. When the Remote Enable input is held LOW continuously, this information is carrieä acrossthe guard

to the bcal/Remote FlipFlop. Control of the flif_flop

is provided by two NAND gates.A LOW RemoteEnable signalresults in a LOW siglralto one input of one of the

SectionIV

gates,and a HIGH signal at one input of the other gate. The Remote Enable signal is gated so that the fwa[ Remote Flip-Flop cannot be changed while remote programinformation is being transferredacrossguard.

4180.0utguardMultiplexer.

4181. This dual4-to-1line multiplexeracceptsg bits of range and function information. Then, when a progam

Execute command is given, this information is transferred serially, two bits at a time, to the two inguard Shift Registers.The Scan A signalis used to selecl the multiplexer outputs. ftan A is applied to one output selectionline, and ScanA divided by 2 is appliedtoihe other line. Figure 4-19 shows the multiplexer output sequence.

SEOUENTIALLOGICINPUTS

PROGRAMEXECUTEH

scat{ c

SEOUENTIALLOGIC -----_-I

OUTPUT

PROGRAMFLAG

 

 

 

 

 

I

OUTPUT

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I

 

 

 

 

l

 

 

 

l

MULTIPLEXERSELECT INPUTS

 

I

 

 

 

 

l

 

 

 

l

s c a N A ( S o )

 

 

-

r - - - l

 

 

 

 

 

t

l

t

t l

 

 

 

 

S C A i l A + 2 ( S , }

 

 

 

 

 

 

 

 

 

 

 

 

r

< t

. ,

: , ' E i

oUTGUARD

 

 

 

6:"

6i";lä

g

MULnpLEXERi"

 

o u r P u r s

 

 

 

g ! 9 ! ; ? ; F i

oaracLocK

 

 

 

r ä , ? r Ei, ä , ) r i S r

 

 

___:-_tt_tl_lt_lt__

 

 

 

 

 

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A[ R.hot.

doCroh

 

 

 

 

'nrdmoron

ronrt.'r.d i

 

 

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crd.

ouo.a

öuri^o

 

 

 

 

 

!.sr.s te.r

tht.

r.nod

ot r,m.-

 

 

 

Figure4-19. RemoteControlTimingDiagram (Option022).

4182. RemoteSequentialLogic.

zl-183.The SequentialItgic is enabledby application '-'of

a ProgramExecute command, which musf go from

signalis invertedand appliedto the Logic.The next time the Scan C signal goesLOW after receipt of a progam Executecommand,the Ingic output alsogoesLOW and remainsLOW until Scan C goesHIGH. Inputs to the

JK flip-flops of the Logic are gated so that only one LOW output is present for each program Execute command, regardlessof its pulse width above 5 ms. While the Logic output is LOW, it enables the Data Clock signaland the ScanA signal,so program informa-

tion may be transferredinto the shift registers.Also, when another logic output signalis LOW, it disablesa gate in the Remote Enable signal line so that the Iocal/Remote selectioncannot be changedduring the ProgramExecuteprocedure.

+184.ProgramFlag.

4-185. The Program Flag signalgoesHIGH to indicate that remote programinformation is beingaccepted,and

+r9