Tektronix 494AP X x x 0 0 X x x 0 1 X x x 1 0, Instrumentbusregisters, DB7-DBO, DB3-DBO

G. Sweep (refer to diagram 3l)

The microcomputerwritesto registers0F and 1F to control sweep rate, mode. holdott, interrupts, and triggEring.

H. Span Attenuator (refer to diagram 32) Registers75 and 76 controlthe spanattenuator.

l. lst LO Driver (refer to diagram 33)

Register72 controlsfunctionson the 1st LO Driver board. RegisterZEis addedto makethe pEAKingcon-

Maintenance- 4g4Al4g4ApServlceVol.l

N. FrontPanel(refer to diagram43)

Readingfrom F4 accessesthe keyboardencoder andtheCENTER/MKRFREQUENCycontrotencoder.

Tabte 6-13

INSTRUMENTBUSREGISTERS

DataBits
7 6 5 4 3 2 1 0	Description

A.Variable Resolution {3F}

Resolution Bandwidth

trol programmable.

J. Preselector Driver (refer to diagram 34)

Register77 controls functionson the preselector Driver. The singlebit DB3 respondson the databus to indicatsthat the board is instaileOwhenthe microcom_ puterperformsa read at F7.

KCENTER/MKR FREQUENCy Controt (reter ro diagram 35)

.R€gisjer70 is provid€d for control functionsand register71 is providedfor data valuesfor centerfre_ quency DAC(s).A read, F0, returns the results of a comparisonof the DAC output voltageand a memory voltage.

L. Auxiliary Synthesizer Control (refer to diagram 371

Register 7D accepts data to set the synthesizer chip, U4041,to output200 MHz to 220MHz in 400 kHz steps.Valuesof R, A, and N are givento determinethe outputfrequencyas givenby the formula

fout : (l/RXNP+A)

where R, the referencedivisionratio,is set at 5 and p is the prescalevalue of 32. N valuesneededare 3.1 through34, while A ranges from 0 to 31. (fable 6_14 showsthe fou, resultsfor givenN andA values.)

M. Phase Lock (refer to diagram 39)

73 acceptsdatato preloadthe +2n counter ,Register

and control the synthesizer.Successivereads from registerF3 obtainstatusand counteroutputs.

After the counteroutput registerselectoris reset, three read cyclesreturn status bits and counterbits in lhg To"l significantbyte and the remainingcounterbits in followingbytes.

1 x x x x 0 0 1

1 x x x x 0 1 0

1 x x x x 0 1 1

1 x x x x 1 0 0

1 x x x x 1 0 1

0 0 0 0 0 x x x

0 0 1 0 0 x x x

0 0 0 1 0 x x x

0 0 1 1 0 x x x

0 0 0 0 1 x x x

0 0 1 0 1 x x x

0 0 0 1 1 x x x

0 0 1 1 1 x x x

0 1 0 0 0 x x x

0 1 1 0 0 x x x

0 x x x x 0 0 0

0 x x x x 0 0 1

0 x x x x 1 0 0

0 x x x x 1 0 1

0 x x x x 1 1 1

B. Log & Video

Ampllfier

DB7-DBO

l x x x x x x x

0 x x x x x x x x l x x x x x x x 0 x x x x x x x x 0 l x x x x x x l 0 x x x x x x 0 0 x x x x

DB3-DBO

IMHz Resolution Bandwidth 100 kHz ResotutionBandwidth 10 kHz Resolution Bandwidth 1 kHz Resolution Bandwidth 100 Hz Resolution Bandwidth

Galn, Levellng

Band 1 Leveling

Band 2 Leveling

Band 3 Leveling

Band 4 Leveling

Band 5 Leveling

Band 6 Leveling

Band 7 Leveling

Band I Leveling

Band 9 Leveling

Band 10 Leveling

0 dB Gain

t0 dB Gain

20 dB Gain

30 dB Gain

40 dB Gain

Video Olfset {78}

LSB- 114dB

Total range- 63.75dB

Modesand ScaleFactorO9)

Pulsestretcheron

Pulsestretcheroff ldentifyoffseton ldentifyoffsetoff Lin

Log Full-screendeflection Log verticalscalefactorin dB/div

6-57