Design Article
Comment
Jim.McLucas
Marian Stofka
Conversion circuit handles binary or BCD
R Srinivasan, R Ramesh, and DK Murthi, National Aeronautical Lab, Bangalore, India
3/1/2012 11:00 AM EST
Originally published in the April 5, 1979, issue of EDN
Systems requiring arithmetic operations on data usually perform those operations in binary form. As a result, they must convert the data to BCD form for display purposes. Address-selection information from digit switches, on the other hand, must be converted to binary form for use in memory-addressing operations.
For applications not requiring fast conversion, a single circuit that can perform both conversions proves adequate. One such circuit (Figure 1) utilizes up/down counters to obtain the desired results. To perform binary-to-BCD conversion, preset the binary value in the binary counter and clear the BCD counter. The binary counter counts down while the BCD counter counts up, and when the binary counter reaches zero, the BCD counter holds. For BCD-to-binary operation, the BCD counter counts down from the BCD value while the binary counter counts up.
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Marian Stofka
3/2/2012 2:14 PM EST
Even at those golden days of digital electronics some 7 IC packages could be saved; while the circuit in Fig. 1 performed the same functions.
Here 7 packages of hex inverters, 7404, plus 2 packages of 13-input NAND gates, 74S133, form two zero-state-detectors.
Both these detectors could be replaced by using the "Borrow" outputs of the most significant synchronous up/down counters, 74193 and 74192; where a Low appears only when reaching zero-state.
My early Design Idea, published in the EDN sometimes in 1980?, had been entitled like: Accurately count asynchronously gated pulses; and concerned right a cascade of 4-bit synchronous BCD counters, the 74192s.
For me the 74193 and especially the 74192 remain Great ICs forever. Nowadays I regret that TI do not produce them in the AHC version.
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Jim.McLucas
3/4/2012 12:02 AM EST
Marian Stofka,
Your circuit "Single circuit converts binary or BCD" was published in the January 5, 1980 edition of EDN. I like it better than the circuit shown above.
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Marian Stofka
3/5/2012 2:19 PM EST
Thank you, Jim.
It seems, you have much easier access to my DIs published in the EDN within 1979? - 1992? than myself.
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Jim.McLucas
3/5/2012 8:29 PM EST
You are welcome, Marian.
I have a copy of your circuit in my "BCD-to-Binary" file in case I need it. Over the years, I have usually saved the EDN "Design Ideas" section of the magazine for future reference.
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