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7000 series readout system: Difference between revisions
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character generator details
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==Layout== | ==Layout== | ||
[[File:Tek7000-readout-positions.jpg|thumb|right|200px|screen layout]] | [[File:Tek7000-readout-positions.jpg|thumb|right|200px|screen layout]] | ||
A total of eight display fields can be superimposed on the CRT picture, four on top and four at the bottom. These are logically associated with the four possible slots in full-size mainframes, with the top field corresponding to the first channel, primary | A total of eight display fields can be superimposed on the CRT picture, four on top and four at the bottom. These are logically associated with the four possible slots in full-size mainframes, with the top field corresponding to the first channel, primary time base or primary function of a plug-in, and the bottom field corresponding to a second channel, delayed timebase, secondary function or unit label. | ||
==Mainframe circuit== | ==Mainframe circuit== | ||
===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, 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. | ||
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[[File:Tek7000-readout-charset.jpg|600px]] | [[File:Tek7000-readout-charset.jpg|600px]] | ||
In time slot 1, special operations can be requested that affect the display in later time slots. These commands are designed to simplify display changes required by external probes that request beam identification or change input sensitivity. The "Identify" command switches to an internal program displaying IDENTIFY instead of any encoded value. Command R3/C1 requests an additional zero to be added starting in time slot 5, R3/C2 adds two such zeroes, R3/C3 shifts the selected prefix one code to the left (i.e. p → n, n → μ, μ → m, m → space), and R3/C4 shifts the prefix and adds a zero. (See the [[Media:Tek-plugin-readout.jpg|encoding circuit of the 7A18 plugin]] for an example implementation.) It is also possible to request a decimal point to be drawn without losing display digits, by encoding row 7 | [[File:7000-readout-chargen-positions.jpg|thumb|300px|right|Character generator matrix positions in 7000 series readout analog character generator ROM]] | ||
In time slot 1, special operations can be requested that affect the display in later time slots. These commands are designed to simplify display changes required by external probes that request beam identification or change input sensitivity. The "Identify" command switches to an internal program displaying IDENTIFY instead of any encoded value. Command R3/C1 requests an additional zero to be added starting in time slot 5, R3/C2 adds two such zeroes, R3/C3 shifts the selected prefix one code to the left (i.e. p → n, n → μ, μ → m, m → space), and R3/C4 shifts the prefix and adds a zero. (See the [[Media:Tek-plugin-readout.jpg|encoding circuit of the 7A18 plugin]] for an example implementation.) It is also possible to request a decimal point to be drawn without losing display digits, by encoding row 7 commands in time slot 1. | |||
The character generators are custom analog chips that provide X and Y output currents for ten characters of up to eight X/Y coordinate pairs inscribing each character. The in-character coordinate points are selected through | ===Character generation=== | ||
The character generators are custom analog chips that provide X and Y output currents for ten characters of up to seven strokes (eight X/Y coordinate pairs) inscribing each character. The in-character coordinate points are selected through a triangular analog signal, not a digital code, which in turn activates one of eight groups of three transistors each generating the X/Y output currents. Each of these groups is fed a constant emitter current (I<sub>E</sub>), and the distribution of this current to the three transistors is controlled by their different emitter areas. The first and second collectors provide X and Y currents respectively, the third ("Z") directs current to the substrate (I<sub>E</sub> - I<sub>X</sub> - I<sub>Y</sub> - I<sub>Z</sub> = 0). Actually, the emitter area itself is not varied in the mask, but out of a fixed number of emitters of equal size, a certain number is connected on each transistor: [[File:7000-readout-chargen-circuit-1.jpg|300px|thumb|ROM circuit for one character (digit "3"). Bases are scanned in turn. The numbers under the emitters indicate how many of the emitters are connected to the common rail. Ten such character circuits plus the scanning (base drive) circuit are integrated in each ROM chip. All X and Y collector outputs are connected across characters and chips.]] | |||
If the bases were controlled by a digital decoder, only one triplet of transistors would be active at any time and only points would be generated on the display. Instead, through an analog driving circuit, gradual cut-over is achieved, i.e. current from one group is reduced while that from the next group is increased, and a linear transition from the first to the second X/Y coordinate pair is displayed as a stroke on the CRT. The actual shape of the base drive voltages has great influence on the proper character rendering (this is explained at length in Gilbert's 1971 SSC paper). | |||
== | ==Plug-in circuit== | ||
A plug-in encodes the desired read-out information either by connecting resistors between the output lines and the time-slot input lines, or by generating equivalent currents. | A plug-in encodes the desired read-out information either by connecting resistors between the output lines and the time-slot input lines, or by generating equivalent currents. | ||
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==Probe interface== | ==Probe interface== | ||
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 | 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 x10 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== | ==Custom chips== | ||