NAND Gate Function in LC78621 DOUT

Jay · 18th November 2005, 03:58 AM

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???

rfbrw · 18th November 2005, 04:14 AM

Off switch ?

Jay · 19th November 2005, 03:52 PM

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

18th November 2005, 03:58 AM	#1
Jay diyAudio Member Join Date: Feb 2003 Location: Jakarta	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???

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Problems adding Digital Out to Laserdisc player (LC78621 chip)	Hybrid fourdoor	Digital Source	9	30th January 2009 08:30 AM
Gate capacitance and gate charge	rtarbell	Parts	1	22nd January 2007 05:11 PM
Amp Will Not Function	prorms	Solid State	16	2nd December 2006 08:26 PM
Why this amp does not function ?????	PicancoNet	Solid State	10	23rd January 2004 04:45 PM
best way to generate Gate-Drain or Gate-Source short in electret capsule JFET?	capslock	Parts	2	27th September 2002 08:07 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

18th November 2005, 04:14 AM	#2
rfbrw diyAudio Member Join Date: Oct 2001 Location: .	Off switch ?

19th November 2005, 03:52 PM	#3
Jay diyAudio Member Join Date: Feb 2003 Location: Jakarta	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