Arpad Since Keith was having issues getting a good low I suspect his new driver has a much faster edge than his old 5V driver. Faster edges can cause all kinds of SI issues. And many drivers are asymmetric in their edge rates where the falling edge is much faster than the rising. I'm also curious if Keith even needed to go through this exercise. Many modern 3.3V receivers are 5V tolerant... And if the new driver has a "TTL" type output the output level will not drive all the way to 5V. Just a thought. Tom Dagostino Teraspeed Labs 13610 SW Harness Lane Beaverton, OR 97008 503-430-1065 tom@xxxxxxxxxxxxx www.teraspeed.com Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 401-284-1827 www.teraspeed.com -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Muranyi, Arpad Sent: Friday, September 10, 2010 12:02 PM To: Muranyi, Arpad; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Level Translator parts To add to my previous posting, now that I think of it, the parts didn't even have to be Bipolar. Chip designers started to make output stages with CMOS pullup transistors with their substrate tied to 5 V while the channel was tied to 3.3 V. This would active the parasitic diode only above 5 V, in other words the clamping action only started to kick in above 5 V. The result was the same, the T-line looked unterminated to signals above 3.3 V and they rang like crazy. The same thing could also happen with an N-channel pullup, which acts like the Bipolar emitter follower I talked about before... Arpad ================================================================ -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Muranyi, Arpad Sent: Friday, September 10, 2010 1:47 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Level Translator parts Keith, I am not familiar with the ST2378 part, and glancing at the data sheet didn't reveal to me whether it has a CMOS or Bipolar output stage. Do you know what technology this part is made with? The reason I am asking this question is because I have seen nice ringing signals with Bipolar devices in the days when the signals were going down to 3.3 V from 5 V and people started using "5.0 V safe 3.3 V" chips. The pullup transistor being an emitter follower would shut down when the signal would go above 3.3 V, which means that the line looks like as if it was completely unterminated at those higher voltages. This high impedance, open ended line rang like a bell with a nice overshooting signal going above 3.3 V. I suspect you may be running into a similar situation if this part behaves similarly... On the other hand, if you are observing the ringing at its input side, the question is what voltage rail does the input's clamping clamp to? If they are clamping to your 5 V supply rail, once again, your input is high impedance all the way to 5 V, allowing the lower voltage signal to ring way above its signaling levels. Just a couple of clues... Arpad =================================================================== -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of keithK EPD Sent: Friday, September 10, 2010 12:38 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Level Translator parts I just experienced an un-expected signal response. It involved a 5v driver (HCT245), series ferrite, ribbon cable, and a 5v to 3 volt part ST2378 driving a 3volt data bus req'd for the new LCD - this whole thing was due to a display going obsolete and a new one to replace the old one. (bus cycle is around 1usec) So, you think that this would be a simple data bus tranlation part to accomplish the job .... the LCD data bus is bi-directional (r/w, of course) .... On the bi-directional data bus, I got a wonderful ringing on the bus while a write bus cycle was occuring, that didn't allow the bus to find a good low level. Sounds like the signals experienced an open circuit.... the 5 control uni-directional signals to the display behaved as expected. comments / solutions welcome. Keith Kowal 781-593-0199 (h) www.product-designs.com ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu