The Tektronix P7001 is a digitizer, processor, and memory for the 7704A oscilloscope.
The design of the P7001 assumes it will be part of a 7704A system, and that the 7704A will be displaying a steady trace. The vertical and horizonal plug-ins control the beam as they would in any 7000-series scope. The P7001 periodically samples the horizontal and vertical signals simultaneously as they pass from the plug-ins to the vertical and horizontal amplifiers. This allows it to fill the memory with data points represented as coordinate pairs, (x1,y1), (x2,y2), (x3,y3), etc. It is not necessary that x2 be greater than x1, i.e. the samples can be taken out-of-order with respect to their equivalent time in the waveform.
The signal coming from the acquisition unit enters a fast four-diode sample and hold circuit where it is sampled at 150 ksamples/sec. Each sample is digitized using a successive-approximation scheme. The analog to digital converter is made of several chips: a digital to analog converter, a comparator, and control logic.
The P7001 has its own power supply built into it, independent of the power supply in the acquisition unit of the 7704A. It has a backplane with an asynchronous bus and several cards that plug into that bus - sampler, analog to digital converter, memory, external digital interface, and display electronics. Early versions of the P7001 use core memory, later versions use semiconductor RAM. The bus is used for low speed signals. High speed signals are sent through coaxial cables that connect to the cards using Peltola connectors.
The Acquisition Unit of the 7704A, the P7001 Processor, and the Display Unit of the 7704A are connected by the Acquisition-Processor-Display (APD) Interface shown below.