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interconnected sequential elements. Use a K(wait-until) and conventional RTM's to solve this problem.

3. An important factor contributing to the unreliability of the punch mechanism is wear. This can be decreased significantly by having the punch off when not punching. Modify the design so that the punch power is automatically turned on and off when the punch is to be used and is not in use, respectively. The punch requires about four seconds to come to speed when started from rest. As an alternative, a circuit might be designed which senses the Punch Synch pulses and detects when the punch is at speed (at speed, Punch Synch signals should occur each 1/1 10 seconds). Note, the punch should not be immediately turned off if a character is missed, but rather the punch should wait until no characters have arrived for say two seconds since, given that a character has been punched, the probability is high that another character will arrive to be punched shortly thereafter. These circuits can be constructed using either an all digital or a control delay (particularly the integrating delay) approach.

4. Design an interface to control the following asynchronous punch. Assume the punch has similar signals to those in Figure PH-3. Anytime the physical punch is free and turned on for 4.5 ins., punch magnet energizing current can be supplied which signifies that punching is to occur. At the end of the punch cycle the Punch Synch Pulse signifies that the punching is completed, and a new punch cycle can be started. Thus, a "model" for this behavior is that when the punch currents are energized a 1/110 second delay within the punch is evoked, and at the end of the delay the Punch Synch Pulse is emitted by the punch. Why is the design of an asynchronous punch interface fundamentally simpler than the one discussed above?


KEYWORDS: Sampling frequency, punch, analog-to-digital conversion.

A device which can sample an analog waveform a number of times and record the samples in a permanent memory for later analysis is a common scientific instrument. The signal to begin the sampling process is usually evoked externally, and the samples are taken in synchronism with a clock that occurs at the sampling frequency. The inputs to the system are the clock (sampling frequency), the analog signal to be sampled, the signal to start the process, and a signal to denote when the process has been completed. Another necessary input (here an 8-bit number named Sample Identification) identifies the particular set of samples.


Design a system to sample and store values of an analog waveform. This particular problem is derived from an actual one, so values have been fixed for the number of samples, maximum sampling clock frequency, etc. At the end of the discussion extensions are proposed which give an excursion into the design alternatives of the system.

The sampling rate is very high relative to the rate at which data can be punched on the paper tape. The paper tape punch operates at approximately one 8-bit character each 1/110 second (i.e., ~10 ms./ character). The minimum sampling time is the time of the analog-to-digital conversion plus the time to store the samples in memory in this design. (The design could be modified to operate at a still higher rate.)



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