7000 series readout system: Difference between revisions

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{{Instrument Sidebar
|class=Subsystem
|manufacturer=Tektronix
|series=
|model=7000-series readout system
|summary=
|image=Tek-7000-readout-board.jpg
|caption=Classic 7000 series readout board (analog ROMs)
|introduced=1969
|discontinued=1992
|designers=Barrie Gilbert
|manuals=
}}
For the [[7000-series scopes]], a system was required to display the instrument state such as input range, time/div etc. alongside or within the display.  Earlier solutions had included fiber-optical/mechanical displays to the side of the CRT such as those in the [[576|576 Curve Tracer]].
For the [[7000-series scopes]], a system was required to display the instrument state such as input range, time/div etc. alongside or within the display.  Earlier solutions had included fiber-optical/mechanical displays to the side of the CRT such as those in the [[576|576 Curve Tracer]].


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A sliding switch on the analog ROM readout board (internal to the scope) allows the operator to select "gate triggered" mode, in which the readout signal is produced only after a sweep has occurred.  The advantage of this mode is that the beam is not interrupted while drawing the signal, however, if no sweep occurs there is no readout, and if the sweep is slow, the readout flickers.
A sliding switch on the analog ROM readout board (internal to the scope) allows the operator to select "gate triggered" mode, in which the readout signal is produced only after a sweep has occurred.  The advantage of this mode is that the beam is not interrupted while drawing the signal, however, if no sweep occurs there is no readout, and if the sweep is slow, the readout flickers.


In certain mainframes such as the [[7844]], [[7904A]] and [[7104]], turning the display intensity control past the maximum intensity setting switches readout into pulsed mode.
In certain mainframes such as the [[7844]], [[7904A]], [[7934]], and [[7104]], turning the readout display intensity control past the maximum intensity setting switches readout into pulsed mode.
Depending on a second switch, readout occurs at the end of the sweep ("+ GATE") or when triggered by a back-panel "Graticule/Readout Single Shot" input.  These scopes also have a "manual readout" button and similar controls for pulsed graticule illumination.
Depending on a second switch, readout occurs at the end of the sweep ("+ GATE") or when triggered by a back-panel "Graticule/Readout Single Shot" input.  These scopes also have a "manual readout" button and similar controls for pulsed graticule illumination.


===Scanning===
===Scanning===
The oscilloscope readout system produces a pulse train consisting of 10 successive negative-going pulses representing a possible character in a readout word, and is assigned a time-slot number corresponding to its position in the word.  Each time-slot pulse is output at -15 V onto one of ten lines, labeled TS-1 through TS-10 (Time Slots 1 through 10), which are connected to the vertical and horizontal plug-in compartments.
The oscilloscope readout system produces a pulse train consisting of 10 successive negative-going pulses representing a possible character in a readout word.  Each time-slot pulse is output at −15 V onto one of ten lines, labeled TS-1 through TS-10 (Time Slots 1 through 10), which are connected to the vertical and horizontal plug-in compartments.


Two output lines, row and column, are connected from each channel (two channels per plug-in compartment) back to the oscilloscope readout system.  Data is encoded on these output lines as a pair of analog current sequences in 100 μA steps from 0 to 0.9 (rows) / 1.0 (columns) mA, which can address a matrix of 11 × 10 positions.  In this matrix, rows 1, 2, 4, 5 and 6 correspond to characters whereas others are used to encode instructions:
Two output lines, row and column, are connected from each channel (two channels per plug-in compartment) back to the oscilloscope readout system.  Data is encoded on these output lines as a pair of analog current sequences in 100 μA steps from 0 to 0.9 mA for rows and 0 to 1.0 mA for columns, the combination of which can address a matrix of 11 × 10 positions.  In this matrix, rows 1, 2, 4, 5 and 6 correspond to characters, whereas other rows are used to encode instructions:


[[File:Tek7000-readout-charset.jpg|center|600px]]
[[File:Tek7000-readout-charset.jpg|center|600px]]
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===Probe interface===
===Probe interface===


Most 7000 series plugins have [[BNC connector with readout ring|rings around the BNC input sockets]] that allow attached probes to interface with the readout system.  The probe connector includes a contact pin connecting this ring.  A resistor connected to ground encodes the probe attenuation, e.g. 11 kΩ indicates a ×10 probe and 6.8 kΩ a ×100 probe.  If the probe includes an Identify switch at the tip, this connects the readout pin directly to ground. The [[Media:Tek-plugin-readout.jpg|plug-in circuit]] uses the shift instructions in time slot 1 to implement the change of range.
Most 7000 series plugins have [[BNC connector with readout ring|rings around the BNC input sockets]] that allow attached probes to interface with the readout system.  The probe connector includes a contact pin connecting this ring.  A resistor connected to ground encodes the probe attenuation, e.g. 11 kΩ indicates a ×10 probe and 6.8 kΩ a ×100 probe.  If the probe includes an Identify switch at the tip, this connects the readout pin directly to ground.  
 
The [[Media:Tek-plugin-readout.jpg|plug-in circuit]] uses the shift instructions in time slot 1 to implement the change of range, which is done by adding 100 μA (1 step) to the column current in time slot 1 for a ×10 probe, or 200 μA (2 steps) for a ×100 probe.  For example, if the encoded unit was 100 mV, TS4 would encode a "1" digit, TS-8 the "m" prefix, and TS-1 the "add two zeros" command (R3/C2).  Connecting a ×10 probe adds 100 μA in TS1, selecting the "shift prefix left" command (R3/C3) instead of "add two zeros".  This drops the extra zeros and changes the prefix "m" to none, thus the display changes to "1 V".  With a ×100 probe, the command selected would be "shift prefix left and add one zero" (R3/C4) and the resulting display becomes "10 V".


===Complex plugins===
===Complex plugins===
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The [[067-0905-99]] "Readout Exerciser" is a test fixture for the readout system.
The [[067-0905-99]] "Readout Exerciser" is a test fixture for the readout system.


==Implementation==
==Implementation==
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===7854===
===7854===
The [[7854]] contains a microprocessor controlled 40x16 character display generator which is also used to display plugin readout data.  The readout interface therefore contains only the column driver, multiplexer and A/D section but not the character generator - it only feeds readout data to the microprocessor.
The [[7854]] contains a microprocessor-controlled 40x16 character display generator which is also used to display plugin readout data.   
The readout interface therefore contains only the column driver, multiplexer and A/D section but not the character generator - it only feeds readout data to the microprocessor.


===EPROM-based Readout Board===
===EPROM-based Readout Board===
[[File:EPROM based 7000 series readout board.jpg|400px|right]]
[[File:EPROM based 7000 series readout board.jpg|400px|right]]
Towards the end of the 7000 series lifespan, in the 2nd half of the 1980s, a re-designed readout board
Towards the end of the 7000 series lifespan, in the second half of the 1980s, a re-designed readout board (Tek part number 670-8622)
(Tek part number 670-8622) was introduced, in which the character generator is based on digital values stored in a 2732 EPROM instead of Gilbert's analog ROMs. This board was installed e.g. in the [[R7103]] and [[7904A]] and still used some of the Tek-made readout ICs like the timing generator. The design is similar to the readout mechanism in the [[2465]] series.
was introduced, in which the character generator is based on digital values stored in a 2732 EPROM instead of Gilbert's analog ROMs,
with the number of display points increased to up to 16 per character.  
 
This board was installed e.g. in the [[7934]], [[R7103]], and [[7904A]] and still used some of the Tek-made readout ICs like the timing generator.  
The design is similar to the readout mechanism in the [[2465]] series.


The number of display points was increased to up to 16 per character. The presence of this board can be detected from the outside by looking at the readout characters which are straight up but were italicized in the analog version (which was done the analog way too, by adding some 10% of the vertical signal to the horizontal channel).  The character style itself is also different — for example, the "V" in the classic board has just two straight lines, whereas they are angled in the digital version.
The presence of this board can be detected from the outside by looking at the readout characters which are straight up but were italicized  
in the analog version (which was done the analog way too, by adding some 10% of the vertical signal to the horizontal channel).   
The character style itself is also different — for example, the "V" in the classic board has just two straight lines, whereas they are angled in the digital version.


:{|
:{|
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===Microcontroller-based Readout Board===
===Microcontroller-based Readout Board===
Finally, from 1989/1990 on, a third generation readout board designed around an 80C31 micro-controller replaced the previous versions in the last series of [[7104]], [[R7103]], [[R7844]], [[7904A]], [[7603]] and [[7623B]] models. This version no longer used any Tek-made special ICs, manufacture of which had been discontinued by that time. The board is part SMD, part through-hole. It is described in [http://w140.com/Tektronix_7904A_OCRed_by_Tabalabs.pdf this version of the 7904A manual] (pages 288 through 291 describe the EPROM version above, while the 80C31 version is shown on pages 380 through 391).
Finally, from 1989/1990 on, a third generation readout board designed around an 80C31 micro-controller replaced the previous versions in the last series of [[7104]], [[R7103]], [[R7844]], [[7904A]], [[7603]] and [[7623B]] models. This version no longer used any Tek-made special ICs, manufacture of which had been discontinued by that time. The board is part SMD, part through-hole.  
It is described in  
[[Media:070-4593-00.pdf|this version of the 7904A manual]]
(pages 288 through 291 describe the EPROM version above, while the 80C31 version is shown on pages 380 through 391).


<gallery widths=300 heights=300>
<gallery widths=300 heights=300>
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7000-readout-ctl-3.jpg |  
7000-readout-ctl-3.jpg |  
Microcontroller based readout board block diagram.jpg | Block diagram  
Microcontroller based readout board block diagram.jpg | Block diagram  
Late 7603 with digital readout.jpg | Late model [[7603]] with μP readout
</gallery>
</gallery>


==Literature==
==Literature==
* Barrie Gilbert, ''[http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=1050157&url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F4%2F22519%2F01050157.pdf%3Farnumber%3D1050157 Monolithic Analog READ-ONLY Memory for Character Generation]'', IEEE J. of Solid-State Circuits, 1971.
* Barrie Gilbert, ''[https://ieeexplore.ieee.org/abstract/document/1050157 Monolithic Analog READ-ONLY Memory for Character Generation]'', IEEE J. of Solid-State Circuits, 1971.
* [[Patent US 3651510A|US Patent 3,651,510, ''Character generator apparatus'']]


==Links==
==Links==
* [http://www.amplifier.cd/Test_Equipment/Tektronix/Tektronix_7000_series_mainframe/rep-und-kal-7603/Reparaturbericht%20TEKTRONIX%207603.htm Repair of readout and installation of readout board in another scope] (many photos, German text)
* [http://www.amplifier.cd/Test_Equipment/Tektronix/Tektronix_7000_series_mainframe/rep-und-kal-7603/Reparaturbericht%20TEKTRONIX%207603.htm Repair of readout and installation of readout board in another scope] (many photos, German text)
* [http://www.electronics-related.com/sci.electronics.design/thread/116046/readout-pin-on-oscilloscope-probes.php Thread about probe readout details]
* [http://www.electronics-related.com/sci.electronics.design/thread/116046/readout-pin-on-oscilloscope-probes.php Thread about probe readout details]
* [[Media:7000 series scale factor readout.pdf|Tektronix 7000 Series Scale Factor Readout (PDF, OCR)]]
* [[7000 Series plug-in interface]]


==Character code table==
==Character code table==
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</div>
</div>


==Font comparison==
<gallery>
Font_160-2997-00.pdf|Font of the 1984 EPROM readout
Font_160-2997-01.pdf|Font of the 1986 EPROM readout
Font_160-2997-xx.pdf|Font comparison 1984 vs 1986 EPROM readout
</gallery>
{{Custom ICs|7000 series readout system}}


[[Category:7000 series scopes]]
[[Category:7000 series scopes]]