Where to get power for 7" display?
Kevin McGrath
I did have to order a longer display cable (I ordered a 300mm and 500mm just to see which one works best for a rack).
Am I in uncharted territory by going with the Touch Display 2? Rack kit #279 is coming along nicely, I'm at the lights/switches test phase of the build, but I need to figure out how to get the display powered and get a longer display cable before I can run the tests comfortably.
John Stout
Bill E
John Stout
Kevin McGrath
Thanks Bill for the suggestion about where to put it, I think I like that much better than hiding behind the speakers. The touch seems to work fine on the display, and that's what I wanted too, to be able to use the touch to manage the Pi, but also I'm looking forward to the light pen simulation. Speaking of which, I can find no documentation on how to actually use the light pen. I assume you'll need to write some code to sweep a dot across the screen until it finally hits the pen when the button on the pen is pushed? The little that is in the docs seem to imply that it "captures" the last X, Y where it sensed a light pulse which you then read (using some unknown instruction)? But, how does the light pen notify the PDP-1 that the button has been pressed on the pen? I'm guessing that it wouldn't be too hard to simulate a touch on the screen (within the display area) being a light pen button press, which then triggers the code to sweep a dot to find where the light pen is, and that could just be the touch coords. It's odd that I can find nothing in the docs about new instructions for the pen though.
Touch input would be fantastic to add to the PiDP-1 though, pretty much the start of interactive graphics so it's historically significant too.
Unibus
My PiDP-1 Rack version is running a Raspberry Pi 5 with its power supply, This was configured with a Pi fan as a precaution but I have only ever heard the fan run for a few seconds during boot phase. The PiDP-1 has always had the tiny Pi fan so I don't know if it has ever been needed The Pi has an ethernet connection, dual HDMI displays (7" plus external monitor), dual passive USB hubs, keyboard and mouse. This configuration may be among the highest current loads.
- The external HDMI is wired through a video (HDMI) capture interface that refuses to capture the HDMI stream. The video capture software complains that the Pi's default HDMI video rate is too slow to capture even though the external monitor has no problems. Solution may be the other HDMI capture interface from another manufacturer I have gathering dust somewhere.
- The dual display can have layout problems when swapping between displays.
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Unibus
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Unibus
Type 30 Precision CRT Display
System #20 (30-G, 30-H)
System #33 (30K)
System #45 (30A)
System #55 (30-G)
Type 33 Digital Symbol Generator1, 1964, Page 1-5
The CRT housing rotates and tilts to allow a good optical presentation of the display. The housing contains the CRT; the mount for the CRT, deflection yoke, and focus coil; a four module mounting box {row D}; the CRT component mounting plate; and the light pen gain control potentiometer. The cables for the CRT go through the mounting pipe.
Instruction(s)
dpy – Display One Point On CRT
Type 31 Ultra Precision CRT Display
System #20 (31-A2)
F-12 PDP-1 Price List, June 1964
Instruction(s)
dpp – Display One Point on Ultra Precision CRT
Type 32 Light Pen
F-15(30E) Type 30 Precision CRT Display, 1963, Page 1-3
Type 33 Digital Symbol Generator1, 1964, Page 1-5
The CRT housing rotates and tilts to allow a1good optical presentation of the display. The housing contains the CRT; the mount for the CRT, deflection yoke, and focus coil; a four module mounting box {row D}; the CRT component mounting plate; and the light pen gain control potentiometer. The cables for the CRT go through the mounting pipe.
Indicators
F-15(30E) Type 30 Precision CRT Display, 1963, Page 1-4
Current state of the coordinate address is shown on two rows of ten lights. A row of four lights indicates the status of the Light Pen and Intensification circuits. A single light indicates the existence of a Need-A-Completion command.
Output Signals
F-15(30E) Type 30 Precision CRT Display, 1963, Page 2-2
If the Light Pen is used and if it has seen a spot during the display period, a pulse similar to the display completed pulse will be produced. This pulse will occur at the same time as the display completed pulse. In addition, a -3 volt level is produced starting at this time and lasting until the next clear pulse is received.
F-15(30E) Type 30 Precision CRT Display, 1963, Page 3-2
The coordinate location (address) information for the displayed spot is determined by the contents of two 10-bit binary words, one for the horizontal coordinate and one for the vertical coordinate. Each word uses the l's complement, in which 1000000000 is -511 or the smallest number, and 0111111111 is the maximum number, +511. The bits are applied as gating levels to the two Buffers. When the Type 30 is controlled by DEC's PDP-1 computer, the two address words are applied in succession by two pairs of memory cycles.
In the next (fifth) memory cycle the computer supplies an IOT instruction which causes the clear and load pulses to be applied to the Coordinate Transfer Circuit, and usually the three intensity level bits to the Status and Intensity Circuit. The load pulse causes the two coordinate words to be transferred into the Buffers and starts the display cycle.
During the first 35 microseconds of the display cycle the output of the Buffers is converted into equivalent analog voltages and applied to separate Deflection Amplifiers through Compensation Networks. At the end of this time the CRT is unblanked for 10 microseconds and a spot of light appears on the screen at the location specified by the two coordinate address words. The intensity of the spot is controlled by the Intensity Bias Circuit.
At the end of the display cycle the Status Circuit generates a negative pulse which is returned to the computer. A second pulse and a negative level will also be generated if a Light Pen has seen the displayed spot.
Light Pen Status
F-15(30E) Type 30 Precision CRT Display, 1963, Page 3-11
At the end of each display cycle a negative Display Done Pulse (DDP) is applied to an inverter gate in a Type 4603 Pulse Amplifier module. This inverter gate is controlled by another inverter which receives the light pen gate signal. When a Type 32 Light Pen is used and the pen sees the displayed spot, it produces a -3 volt saw a spot (sas) level during and slightly after the spot's display period. This turns on the inverter, enabling the inverter gate and allowing the DDP pulse to activate the pulse amplifier. The pulse amplifier turns on a third inverter which complements the light Pen Status Flip-Flop, thereby producing a negative Light Pen Status (LPS) level that is returned to the computer.
The LPS level is also applied to another inverter in a Type 4604 module which conducts and activates a pulse amplifier. This pulse amplifier produces the positive Light Pen FIag (LPF) which is returned to the computer.
Adjustments
F-15(30E) Type 30 Precision CRT Display, 1963, Page 4-2
Light Pen Gain - Located underneath the right front of the CRT housing. Clockwise rotation increases gain.
Type 33 Symbol Generator
System #55
F-12 PDP-1 Price List, June 1964
Description
The Type 33 Digital Symbol Generator is an ancillary item designed and manufactured by Digital Equipment Corporation for use with their PDP-l and PDP-4 computers. It is used in conjunction with either a Type 30G or a Type 30H Precision CRT Display to present alphanumeric symbols on the CRT with a minimum of computer time and programming. The operation of the display is unaffected in its normal point plotting mode.
The Type 33 controls the operation of the display in the symbol generating mode. It enables the display to show any symbol that can be made with a 5 by 7 dot matrix, at any selected location on the raster. Once a location has been selected, symbols are automatically positioned on a horizontal line, and each succeeding symbol is automatically moved one position to the right. Any symbol can be dropped to a subscript position at any location with no extra commands. A separate format command is used to select one of four matrix sizes and to space one position to the right.
The display itself uses two 10-bit binary words and a display command to show a single dot at some location within a 1024 by 1024 dot square raster. Successive dots may be displayed at any random position at a 20 kilocycle rate. Eight different levels of intensity can be selected by the computer in both the point plotting and symbol generating modes.
The Type 30G may be used with either the PDP-lor PDP-4 computers, while the 30H may be used only with the PDP-l. Aside from a few minor circuit changes to accomodate the different interface, the Type 30H has the ability to duplicate its presentation on an auxiliary highspeed oscilloscope such as the Tektronix RM 503. Both displays can use a Light Pen, either Type 32 or Type 370, to identify specific displays, and operate with either centered or offset rasters. Table 1-1 lists the operating characteristics of the Type 33 with either display.
PHYSICAL
The Type 33 Symbol Generator is an integral part of either a Type 30G or Type 30H
Point Plotting Mode
In the point plotting mode, a spot of light is displayed on the screen of the CRT for 3 microseconds somewhere within a 9-3/8 inch square raster in each display cycle. The location of the spot is controlled by four currents flowing through a deflection yoke, and is directly related to the numerical value of two 10-bit binary words. The computer loads one of these binary words into the Y buffer, and the other into the X counter (which acts as a buffer). The voltage of each bit in both of these words is amplified and standardized, and then each word is converted into an equivalent analog voltage by a digital-to-analog converter. Each analog voltage controls the current through two opposing deflection coils in the deflection yoke, whose resultant magnetic field deflects the electron beam to its preselected point. The spot is not produced until 35 microseconds after the binary words are loaded into the buffers to eliminate any movement of the spot. The lOT command in the PDP-l that transfers the two words to the buffers and initiates the display cycle also selects the level of intensity of the displayed spot.
Symbol Generating Mode
Operation in the symbol generating mode is more complicated. The computer determines the location of the left end of a horizontal line along which symbols are to be plotted and loads this location into the X counter and Y buffer as in the point plotting mode, but does not initiate the 35-microsecond setup delay or permit a display. It next determines the intensity level, whether incrementing for additional symbols is needed, and the character size format for the line; and loads this information into the intensity and format buffers. Then it selects the first half of the particular symbol word to be generated and determines if it is to be a subscript, and loads this into a shift register with a command that initiates the symbol matrix plotting sequence. The computer must now select the last half of the symbol word and wait for the Type 33 to give a completion signal when the first half of the symbol word has been displayed, then transfer the last half of the symbol word to the shift register with a command that starts the symbol matrix plotting sequence again from the place where it left off. The Type 33 will again return a completion signal to the computer when it has finished displaying the character and has incremented the X counter to the beginning location of the next symbol.
The Type 33 automatically generates a 5 by 7 matrix of some predetermined size with the lower left corner at a predetermined starting location. It moves the position of the electron beam in sequential increments from 0 to 34 as shown, with 2 microseconds required for each move. A symbol is generated by intensifying the electron beam for 3 microseconds when it is located at the desired position. This requires two l8-bit words per symbol from the computer, with a 1 in each bit for an intensified location and a 0 in each bit for a blanked location. The extra bit-17 in the first half of the symbol word, is not displayed but is used as a control level to select normal or subscript locations for the matrix.
Starting Location
Before a symbol or line of symbols can be displayed, it is necessary to specify the location of the lower left corner of the first symbol on the line. This is accomplished by having the computer load the X coordinate of the location into the X counter and the Y coordinate of the location into the Y buffer.
Starting Coordinate Loading Program
The PDP-l has two registers available for in-out transfer of digital information, as well as a register that makes some of the bits of the in-out transfer (lOT) command available as control levels. This makes it possible for both coordinate address words and all necessary control pulses and levels to be transferred to the Type 33 during the two memory cycles of the lOT operation. However, each of the two registers - the accumulator (AC) and the input-output (I-O) - must be loaded from memory separately before the lOT command. Each loading operation takes two memory cycles; so a total of 30 microseconds is necessary for the computer to retrieve the coordinate address words and loading command from memory and effect their transfer to the Type 33.
Mnemonic |
Code |
Time (µsec) |
Operation |
Explanation |
lac X |
020xxxx |
10 |
C(xxxx) => C(AC) |
X coordinate word in xxxx loaded into AC |
lio Y |
022yyyy |
10 |
C(yyyy) => C(I-O) |
Y coordinate word in yyyy loaded into I‑O |
sdb |
0722007 |
10 |
C(AC)
=> C(XC) |
All display buffers cleared, X coordinate word transferred into X counter, Y coordinate word transferred into Y buffer, deflection setup delay and intensification inhibited, intensity buffer loaded for normal intensity level |
Only the first ten bits of the AC register, AC0-9 are used for the X coordinate word. The AC1-9 bits are ground for logic 0 and -3 volts for logic 1; therefore each of these bits must be inverted before application to the X counter2. The first ten bits of the I-O register, I-O0-9 are used for both the Y coordinate word and as part of the character word. The I-O register bits are -3 volts for logic O and ground for logic 1. The IOT command produces a clear display pulse (CDP) at TP7 and a load display pulse (LDP) at TP10, and makes bit 7 and bits 9, 10, and 11 of the command available from the memory buffer (MB). Bit 7 (MB7) is the display (DPY) level, permitting a display when it is a logic 0 (MB07) and inhibiting a display when it is a logic 1 (MB17). The other three bits control the intensity level, which is normal when their octal number is 0. Increasing the number to 38 progressively increases the intensity, while 48 drops it to the minimum value. Further increases slowly raise the intensity towards normal again. These bits form the third digit from the right in the instruction word.
Intensity Buffer
Eight different levels of intensity are possible with the Type 30G or the Type 30H. These levels correspond with the numerical value of a 3-bit l's complement binary word supplied by the computer. The intensity buffer stores this word and generates appropriate control signals for the intensity bias circuit until the computer next clears the buffer.
The 3-bit binary word which specified the intensity level is obtained from bits 9,10, and 11 of the lOT instruction (MB9-11). These are the INT-l, INT-2, and INT-3 signals, respectively. The lOT command which generates these signals also produces a clear pulse (CDP) 1.1 microsecond later, and a load pulse (LDP) 3.3 microseconds later. The negative CDP pulse triggers a Type 4606 Pulse Amplifier, which produces a positive pulse that is applied to the direct clear inputs of the intensity buffer flip-flops and the light pen status flip-flop, setting them to their ZERO states.
Character Size
Four different matrix sizes are selected by bits SR16 and SR17. Since these bits are used in both the vertical coordinate word and the two halves of the character word, they must be loaded into the format control buffer by a separate operation. Note that the incrementing control bit, SR15, is loaded at the same time.
Mnemonic |
Code |
Time (µsec) |
Operation |
Explanation |
lio F |
022ffff |
10 |
C(ffff) => C(I-O) |
Format word in ffff loaded into I-O |
glf |
0722026 |
10 |
C(IO) => C(FB) |
Format word transferred into format buffer |
Incrementing and Spacing
When successive symbols are to be displayed on the same horizontal line, the Type 33 automatically moves the starting location of the next symbol matrix to the right. The next symbol can then be initiated by loading and displaying the first half of the character word, or the starting location can be moved one more position to the right without a display by a spacing command. This avoids the time required to retrieve words from memory and set up the deflection currents.
If the next display is not going to be adjacent to the previous symbol, SR15 is a 0. This sets incmt to the ZERO state and makes inc -3 volts, disabling the inc-X circuit and enabling a gate which will stop the matrix plotting sequence after the last point is plotted.
Space Command
In order to space the symbol matrix one character to the right, the incmt flip-flop must be set to ONE and then a separate space command must be issued. This is called gsp (0720026). A counting sequence is then initiated whic h increments the X counter 4, 5,6, or 7 times, depending on the size specified by the CS flip-flops. A DDP pulse is produced by the last incrementing pulse.
NOTE: The space command will transfer the contents of the I-O register to the shift register and any ones in the seven more-significant bits will cause the spot to be intensified. The computer's register should be cleared before the space command occurs to avoid extra displays.
Instructions
gdb – Load Buffer, No Intensity
glf – Load Format
gpl – Generate Plot left
gpr – Generate Plot Right
gsp - Space
1In the original text the operation C(IO) => C(YB) was written as C(AC) => C(YB). This implies C(IO) => C(AC) => C(YB). The contents C(AC) after the sdb instruction should be confirmed through the Computer History Museum.
2Type 33 Symbol Generator Manual, 1964, Page 3-4, Figure 3-2 Type 33 Symbol Generator Block Diagram, Note 1 includes:- “When used with the PDP-1, the vertical address word is applied to the X counter directly and the counter inverters and three intensity inverters {not shown} are used.”. Therefore the binary inversion discussed is a hardware function.
Type 370 High Speed, Photomultiplier Light Pen
F-12 PDP-1 Price List, June 1964
The high-speed light pen is a photosensitive device which senses displayed points on the face of the CRT. The Type 370 uses a fiber optic light pipe and photomultiplier system, which gives the pen a response time approximately five times faster than that of a photodiode. If the pen is held in front of a point displayed on the face of the CRT, it transmits a signal which sets the display flag to 1. The Type 370 is equipped with a mechanical shutter which prevents the sensing of unwanted information while positioning the pen. Variable fields of view are obtained by means of a series of interchangeable tips with fixed apertures.
A.1 INTRODUCTION
The function of the light pen (see Figure A-1) is to detect light pulses appearing on the face of a display oscilloscope. The light pulses are converted into electrical pulses by the light pen circuitry and interpreted by the computer program into coordinate locations on the face of a scope. These locations are then treated in accordance with the computer program.
The shutter for the light pen is located on the pen itself. There are six fixed apertures available, ranging from 0.300 inch to 0.050 inch. The amplitude of the output signal is adjustable; rise and fall times of the output signal are primarily dependent on the rise and decay times of the CRT phosphor.
A.2 PHYSICAL AND ELECTRICAL SPECIFICATIONS
|
|
|
|---|---|---|
Light Pen |
Length: |
8-1/2 inches |
|
Diameter: |
5/8 inch |
Light Pipe |
Length: |
4 feet Output |
Power Supply |
Depth: |
1-3/4 inches |
|
Height: |
4-1/4 inches |
|
Width: |
8-1/4 inches |
Operating Temperature |
|
50°F to 100°F |
Input Power |
|
-15 volts at 700 milliamperes |
Input Light (Minimum) |
|
300 foot-lamberts |
Spectral Response |
|
4300 to 5600 angstroms |
Output |
|
Approximately 0 to -6 volts |
|
|
(This output may be used to drive the base input of an inverter such as the one utilized in the DEC Type 4105 Module. If the phosphor is fast enough, the output may be differentiated. Use of a pulse amplifier with a differentiating input, such as the DEC Type 4604, produces a standard output pulse with other DEC Modules. |
A.3 THEORY OF OPERATION
A flexible fiber optic light pipe is combined with a photomultiplier tube to detect points displayed on a cathode ray tube screen. A mechanical shutter in the form of a pen is attached to one end of the light pipe. This shutter prevents unwanted light information from entering the light pipe during pen positioning. To detect displayed points, the pen is positioned and then the shutter is depressed. Light is transmitted through the light pipe to the photo-cathode of the photomultiplier. The amplified signal from the photomultiplier is connected to an emitter follower which acts as an output buffer.
A.3.1 Light Guide
The flexible light guide is constructed of unoriented glass fibers 0.003 inch in diameter. The approximate number of fibers is 1470. The minimum radius of bend is 3/4 inch. For sharper bends, the fibers may be broken. Figure A-2 shows the relative transmission for light of different wave lengths.
A.3.2 Photomultiplier
The photomultiplier operates as follows. Light falling on the light-sensitive photocathode provides sufficient energy to liberate some of the electrons. The freed electrons are attracted towards an electrode with a potential more positive than the photocathode. Each electron striking this secondary electrode (dynode) frees more electrons which are attracted to the next more positive dynode. This
process is repeated for a number of stages. The electrons from the final stage are collected at the anode. Drawing D-370-0-2, page A-7, illustrates the circuitry of the photomultiplier (a 931A tube with an S-4 spectral response). Figure A-3 shows the spectral sensitivity characteristics of a phototube exhibiting an S-4 response.
The 100,000-ohm 1-watt resistor in series with the photocathode partially limits the current through the photomultiplier and dynode resistor string.
A.3.3 Overall Spectral Response
The combination of the spectral responses of the photomultiplier and the light pipe is shown in the composite spectral response of Figure A-4. This is the response of the 370 Light Pen.
A.3.4 Output Circuitry
The anode of the photomultiplier is connected to one end of a potentiometer, the other end of which
is grounded. The amplified current collected at the anode passes through the potentiometer to generate a voltage signal which varies in accordance with changes in load resistance. This signal is applied to the input of an emitter follower to provide driving power and a low output impedance. Drawing D-370-0-2 shows some of the logic connections of the 370 Light Pen for operation with some of the DEC displays.
A.4 MAINTENANCE
Because of the simplicity of the light pen, maintenance is at a minimum. In addition to visual inspection, the high voltage power supply should be checked and adjusted as described below:
To measure the high voltage supply, unscrew the red slug located at the top of the supply. This provides access to the voltage test point. The voltage may be varied by means of the screwdriver slot adjustment. The voltage should not be increased beyond -1250 volts, which is the maximum rating of the photomultiplier. If it is necessary to remove the cover of the supply, disconnect the 7-inch amphenol socket before removing the cover.