Tektronix 494AP DATAinstrumentbus dataquery, InstrumentBusRegisters, Responseto Data query

Malntenance- 494Alttg4ApService Vol. I

DATA(instrumentbus data)query

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Responseto DATA query

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CombinedADDRcommandand DATAcommand

The address command may precede a data com- mandor queryto identifythe instrumentbus locationas part of the same m€ssage.

Enors related to these commandsare 41, invalid DATA or ADDR argument contents, and 42, DATA directionnot compatiblewith ADDRdirection.

InstrumentBusRegisters

Registersprovide the link betweenthe instrument bus and microcomputercontrolledfunctions.The regis- ters are definedhere in the same order as they appear in the Diagramssection.The definitionsare providedto help in constructingDATA commandsand interpreting responsesto DATAqueries.

The datais presentedhereas binary.In somecases

adata value occupies the entire register width; for instance,a value in digital storage. tn other cases, a singlebit or group of bits in the registerforms a code; for instance,the upper five bits in the sweep rate and mode register indicate the sweep timeldivision.The meaningof the data is not fully definedhere; ref€r to the d€scriptionof the circuit module in Section5 for details.

To use the binary codes presentedhere with the DATA commandand query statements,you must con- vert_binary to hexadecimal.The binary code number 01001011i$ usedas an examplein the followingsteps.

1.Groupthe lower four bits and th€ upperfour bits (breakthe data byte in half).

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01001011 01001011

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2.Converteachgroup of four bits to a hexadecimal digit. Hexadecimaldigits range from 0 to F in the sequenc€0123456789A8CDEF.

0100- 4

1011- B (i.e..8+0+2+1-11,whichis hexadecimatB)

3.Group the two hexadecimaldigits together,keep- ing their respectiveplaces.

4 and B mak€the two-digithexadecimalnumber48

The infornationin Table6-13is separatedby regis- ters. The following informationis related to the table informationby leadingalphadesignators.

A. Variable Resolutlon (refer to diagram 20)

The microcomputerwrites to two variableresolution registers. The data MSB steers the other bits that are definedinto the desiredregister.WhenDB7equals1, it steers DBo through DB2 to select the resolution bandwidth.WhEnDB7 equals0, it steers DB6 through DBo to selectthe amountof gain addedin the VR s€c- tion and the bandlevelinggain (gainadjustmentrelated to front-endresponsein each band).Thesetwo func- tions are addressedand set togetherby the samedata byte.

B. Log and Video Amplifier (refer to diagram 23)

There are two registersthat receive data from the microcomputer. One register controls vid€o offset (78) and the other controlsthe displaymodesand the verti- cal scalefactor (79).

C. Video Processor (reler to diagram 24)

Register 7C controls out-of-bandclamping,video filtering,and leveling.

D. Digital Storage, Vertical (refer to diagram 25)

Registers7A and FA on the V€rticalDigitalStorage board transferdisplaydata to and from the microcom- puter for spectrumanalyzerGPIB operations.Register 78 controlsdigitalstoragefunctions.

E. Z-Axis & RF Interface (refer to digram 28)

Register4F on the Z-Axis & RF Interfaceboard enablesZ-axis and RF attenuatorcontrol.RegisterCF reportspowersupplystatus.

F. Crt Readout (refer to diagram 30)

Register5F controlscrt readoutand data steering. Register2F acceptsdatafrom the microcomputer.

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