NAND Gate Function in LC78621 DOUT - diyAudio
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Old 18th November 2005, 03:58 AM   #1
Jay is offline Jay  Indonesia
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Default NAND Gate Function in LC78621 DOUT

In a CDP, digital output is taken from DOUT pin of LC78621E DSP. It is said to be in EIAJ format. This digital signal is then fed to a 2-input NAND Gate (74HC00AP) and then drive a transformer before leaving the enclosure.

Originally I thought that this NAND Gate is for converting another digital format into SPDIF. But I read a thread where the SPDIF can be achieved from the DOUT simply by voltage divider or alike. So I checked the specification of both formats, and found out that they are actually similar bitwise.

So I checked the input pins of the NAND Gate and I saw one input pin grounded. Intuitively I knew that the NAND Gate only pass the signal, so I was confused as of the function of the NAND Gate there. I guessed, may be it is to keep a stabil impedance. But then I read again and found that for NAND operation, LOW+LOW=HIGH! So what is this gate doing there???
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Old 18th November 2005, 04:14 AM   #2
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Off switch ?
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Old 19th November 2005, 03:52 PM   #3
Jay is offline Jay  Indonesia
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Off switch??? I don't have electronics background so I don't really know what kind of switch could exist there. Actually there's ceramic oscillator between the NAND Gate and the transformer. This oscillator puzzles me even more...

But I will bypass most components between the DOUT and CS8414, may be including the transformer. The only thing I can do is try and listen. Cannot calculate, but can listen sounds
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