7000 series readout system: Difference between revisions

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.

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.

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:

Most 7000 series plugins have 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.

====Custom chips====

[[File:7000-readout-diagnostic.jpg|thumb|300px|right|Classic readout board diagnostic display]]

The [[7854]] contains a microprocessor controlled 40x16 character display generator which is also used to display plugin readout.  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.

Towards the end of the 7000 series lifespan, in the 2nd half of the 1980s, a re-designed readout board,

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.

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.

| Analog ROM board      || EPROM 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]] 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).

==Character code table==