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Registered Member #97
Joined: Thu Feb 09 2006, 05:40PM
Location:
Posts: 61
I have having trouble reading the schematic for a quiz bowl circuit. I am confused by the inputs on the D type flip-flop because the names are different from those on the datasheet. What do PRE, D, CLK, CLR mean? Which is clock, reset, data, and set?
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Welcome back. I take it you're a novice with digital electronics.
Component figures in schematic diagrams often don't match those in datasheets. In this case "CLK" is the clock "D" is the data input. "CLR" (clear) is the asynchronous reset. "PRE" (preset) is the asynchronous set.
Not sure what you mean about good circuits and recommendations.
IMHO it makes a good quiz question and isn't hard to set up in real life. The pushbutton input circuits properly never leave CMOS inputs floating.
Comments on the schematic drafting style:
1) Big plus: the pins on device figures are arranged by function instead of physical placement on the packages. Right-to-left orientation of the 4-input And gate is well justified for improved clarity & appearance.
2) Coloring the LED symbols is silly. Obviously intended to suggest different luminous colors, but that use of color in a schematic diagram is unconventional (and irrelevant to the quiz question). Informal designators A, B, C, D are good to support discussion of the circuit behavior.
3) It's a plus that connections for logic power & ground, and unused gate inputs, are explicit. But unused FF input connections are not stated. Writing "0V" as an implicit synonym for ground symbol connection is sloppy. If that text were somehow included in a compilation, the auto-generated netlist would have no connection between the pins with ground symbol and those connected to "0V".
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Quiz bowl circuit
