This is a DEC AX08 Laboratory Peripheral manufactured on October 28th 1970, serial number 327. It has the following functions 9 bit multiplexed input analog to digital (A/D) converter with up to 24 input channels, crystal and R/C clocks, up to 3 adjustable Schmitt trigger pulse input, up to 8 digital pulse inputs, and up to 4 digital outputs. It also had a point plot display output. Digital first started selling these units in 1967.
The point plot output was used to drive an oscilloscope. Later X/Y deflection monitors like VR14 were used. The display is generated by the processor specifying an 9 bit X and Y location and then requesting that a spot be drawn on the CRT at that location. It then repeates this process to draw the entire display with out of a bunch of dots. On the VR14 link above are pictures and videos of the display from the similar VC8E point plot display for the PDP-8/E. The entire display would need to be redrawn at a 30-60Hz rate to prevent flicker.
The successive approximation (more) type of A/D converter uses a digital to analog (D/A) converter as part of its operation. To save cost the same D/A converter is used for the analog to digital converter and the point plot display. The AX08 gives precedence to the A/D conversion so the point plot display can't be refreshed while an A/D conversion was in process.
The timing of the AX08 is either controlled by a crystal clock with a period of 100 microseconds or a RC clock with an adjustable period of 20 microseconds to 2 Seconds in 11 ranges. These clocks can be used for software timing and be used as the A/D converter sample clock.
The Schmitt trigger digital pulse inputs have an adjustable threshold of -.5 to -2.5 volts and a .7 volt hysteresis. A bit in a register is set when they cross the lower threshold generate an interrupt to the processor if enabled. The 8 "contingency" inputs set bits in the external register when they are at ground.
|Power||Type 728 or 779 Power supply
10V TBD A, -15V TBD A
|Operating Temperature||0 to 50C||A/D Converter Specifications|
|Word Length||9 bits|
|Accuracy||+- 1/2 LSB +- .2%|
|Speed||<= 17 microseconds|
|Sample & Hold Speed||full scale track
in 2 microseconds
|Input||+-1.024V full scale
50K input impedance
|Speed||<= 17 microseconds|
|Input Channels||4 standard
|Point Plot Specifications|
|Intensity Control||1 bit standard
3 bits optional
|X & Y Output||0 to -10V|
The following picture links below also have descriptions of what is show in the pictures.
Thumbnail Picture Selector
Front view ( 79K) Rear of front panel (109K)
Top view (167K)
Left side ( 96K) Right side (112K)
Bottom view (233K) Backplane closeup (250K)
Back view ( 71K)
Labels ( 38K)
|1||A401 Sample and Hold|
|2||A601 3 Bit DAC|
|1||A704 Reference Supply|
|1||A706 Power Supply|
|1||R002 Diode Network|
|11||R113 NAND/NOR Gate|
|6||R123 Input Bus Gate|
|17||R202 Dual Flip Flop|
|5||R203 Triple Flip Flop|
|5||R205 Dual Flip Flop|
|3||R302 Dual Delay (One Shot)|
|1||R405 Crystal Clock|
|4||R603 Triple Pulse Amplifier|