Hi Geert, In a prototype I use mixed voltages too.
You should just check the datasheet of the IC you like to use. F.e. I use the 5V LTC1391 (8 channel analog mux), the datasheet says: Vinh must have a minimum of 2.4 V which is great and doesn't need conversion. Even if you want to pull-up, I would suggest you to pull-up to the 3.3 V. The only problem to pull-up to 5V in your case could be that you draw to much current from the I/O pin when set as an output. But the 5K6 you like to use will only draw 0.89 mA when the board tries to output a low level, which wouldn't harm the chip. But again, if it isn't needed, I would just pull-up to 3.3V and all should work fine. Kind regards, Wouter housy[at]telenet[dot]be --- In [email protected], "Geert Vancompernolle" <[EMAIL PROTECTED]> wrote: > > Hey... These are two contradictory answers... ;-)... > > Thanks for the reference document, Al. I'll surely read it and see > how I can *safely* convert from 3.3V to 5V. > > I'm a bit afraid of what Frédéric wrote, when he said he destroyed > already two I/O pins like that. > > Certainly not what I want, of course... > > Best rgds, > > --Geert > > --- In [email protected], SailorAl <sailor_alois@> wrote: > > > > I have not tried what you propose, but from my understanding of 5v > tolerant inputs it should be fine. Here is some additional information. > > http://www.standardics.nxp.com/support/documents/i2c/pdf/an97055.pdf > > > > Al Langer > > > > ----- Original Message ----- > > From: Geert Vancompernolle > > To: [email protected] > > Sent: Friday, December 01, 2006 9:36 AM > > Subject: [foxboard] Output pins 5V tolerant: a question. > > > > > > > > Hi, > > > > I read in the documentation that all pins on the two 40 pin connectors > > are 5V tolerant. > > > > I'm currently using the I2C pins of the connector and they're > > connected to two series resistors of 100 Ohm (one for clock, one for > > data), which are connected to a PCF8574 device. > > > > The PCF8574 device is powered with +5V (also coming from the 40 pin > > connector). The signal levels of the I2C bus are 3.3V at the I2C > > inputs of the PCF8574. I know this is sufficient, but I would like to > > use a pull-up resistor of 5k6 to +5V for both SDA and SCL to increase > > the level to +5V. Like this: > > > > +5V > > | > > _ > > | | > > |_| > > | ___ > > SDA-FOX ------|___|----> SDA-PCF8574 > > > > Same for SCL. > > > > Is this allowed? Will I not harm the I/O ports of the FoxBoard? > > > > Best rgds, > > > > --Geert > > > > > > > > #ygrp-mlmsg { FONT-SIZE: small; FONT-FAMILY: > arial,helvetica,clean,sans-serif}#ygrp-mlmsg TABLE { }#ygrp-mlmsg > SELECT { FONT: 99% arial,helvetica,clean,sans-serif}INPUT { FONT: 99% > arial,helvetica,clean,sans-serif}TEXTAREA { FONT: 99% > arial,helvetica,clean,sans-serif}#ygrp-mlmsg PRE { FONT: 100% > monospace}CODE { FONT: 100% monospace}#ygrp-mlmsg * { LINE- HEIGHT: > 1.22em}#ygrp-text { FONT-FAMILY: Georgia}#ygrp-text P { MARGIN: 0px > 0px 1em}#ygrp-tpmsgs { CLEAR: both; FONT-FAMILY: Arial} #ygrp-vitnav { > FONT-SIZE: 77%; MARGIN: 0px; PADDING-TOP: 10px; FONT-FAMILY: > Verdana}#ygrp-vitnav A { PADDING-RIGHT: 1px; PADDING-LEFT: 1px; > PADDING-BOTTOM: 0px; PADDING-TOP: 0px}#ygrp-actbar { CLEAR: both; > MARGIN: 25px 0px; COLOR: #666; WHITE-SPACE: nowrap; TEXT-ALIGN: > right}#ygrp-actbar .left { FLOAT: left; WHITE-SPACE: nowrap}..bld { > FONT-WEIGHT: bold}#ygrp-grft { PADDING-RIGHT: 0px; PADDING- LEFT: 0px; > FONT-SIZE: 77%; PADDING-BOTTOM: 15px; PADDING-TOP: 15px; FONT- FAMILY: > > Verdana}#ygrp-ft { PADDING-RIGHT: 0px; BORDER-TOP: #666 1px solid; > PADDING-LEFT: 0px; FONT-SIZE: 77%; PADDING-BOTTOM: 5px; PADDING- TOP: > 5px; FONT-FAMILY: verdana}#ygrp-mlmsg #logo { PADDING-BOTTOM: > 10px}#ygrp-vital { PADDING-RIGHT: 0px; PADDING-LEFT: 8px; > MARGIN-BOTTOM: 20px; PADDING-BOTTOM: 8px; PADDING-TOP: 2px; > BACKGROUND-COLOR: #e0ecee}#ygrp-vital #vithd { FONT-WEIGHT: bold; > FONT-SIZE: 77%; TEXT-TRANSFORM: uppercase; COLOR: #333; FONT- FAMILY: > Verdana}#ygrp-vital UL { PADDING-RIGHT: 0px; PADDING-LEFT: 0px; > PADDING-BOTTOM: 0px; MARGIN: 2px 0px; PADDING-TOP: 0px}#ygrp-vital > UL LI { CLEAR: both; BORDER-RIGHT: #e0ecee 1px solid; BORDER- TOP: > #e0ecee 1px solid; BORDER-LEFT: #e0ecee 1px solid; BORDER-BOTTOM: > #e0ecee 1px solid; LIST-STYLE-TYPE: none}#ygrp-vital UL LI .ct { > PADDING-RIGHT: 0.5em; FONT-WEIGHT: bold; FLOAT: right; WIDTH: 2em; > COLOR: #ff7900; TEXT-ALIGN: right}#ygrp-vital UL LI .cat { > FONT-WEIGHT: bold}#ygrp-vital A { TEXT-DECORATION: none}#ygrp- vital > A:hover { > > TEXT-DECORATION: underline}#ygrp-sponsor #hd { FONT-SIZE: 77%; > COLOR: #999}#ygrp-sponsor #ov { PADDING-RIGHT: 13px; PADDING- LEFT: > 13px; MARGIN-BOTTOM: 20px; PADDING-BOTTOM: 6px; PADDING-TOP: 6px; > BACKGROUND-COLOR: #e0ecee}#ygrp-sponsor #ov UL { PADDING- RIGHT: 0px; > PADDING-LEFT: 8px; PADDING-BOTTOM: 0px; MARGIN: 0px; PADDING-TOP: > 0px}#ygrp-sponsor #ov LI { PADDING-RIGHT: 0px; PADDING-LEFT: 0px; > FONT-SIZE: 77%; PADDING-BOTTOM: 6px; PADDING-TOP: 6px; > LIST-STYLE-TYPE: square}#ygrp-sponsor #ov LI A { FONT-SIZE: 130%; > TEXT-DECORATION: none}#ygrp-sponsor #nc { PADDING-RIGHT: 8px; > PADDING-LEFT: 8px; MARGIN-BOTTOM: 20px; PADDING-BOTTOM: 0px; > PADDING-TOP: 0px; BACKGROUND-COLOR: #eee}#ygrp-sponsor .ad { > PADDING-RIGHT: 0px; PADDING-LEFT: 0px; PADDING-BOTTOM: 8px; > PADDING-TOP: 8px}#ygrp-sponsor .ad #hd1 { FONT-WEIGHT: bold; > FONT-SIZE: 100%; COLOR: #628c2a; LINE-HEIGHT: 122%; FONT-FAMILY: > Arial}#ygrp-sponsor .ad A { TEXT-DECORATION: none}#ygrp- sponsor .ad > A:hover { TEXT-DECORATION: > > underline}#ygrp-sponsor .ad P { MARGIN: 0px}o { FONT-SIZE: > 0px}..MsoNormal { MARGIN: 0px}#ygrp-text TT { FONT-SIZE: > 120%}BLOCKQUOTE { MARGIN: 0px 0px 0px 4px}..replbq { } > > > > --------------------------------- > > Everyone is raving about the all-new Yahoo! 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