http://forums.leaflabs.com/topic.php?id=589 A place to share, learn, and grow... en-US Fri, 22 Jan 2016 00:15:17 +0000 http://bbpress.org/?v=1.0.2 q http://forums.leaflabs.com/search.php http://forums.leaflabs.com/topic.php?id=589#post-3283 Sun, 02 Jan 2011 22:49:19 +0000 mikep 3283@http://forums.leaflabs.com/ <p>Cool!<br /> That is good to know ...<br /> Thanks for the update. </p> http://forums.leaflabs.com/topic.php?id=589#post-3279 Sun, 02 Jan 2011 17:28:34 +0000 ianmga 3279@http://forums.leaflabs.com/ <p>Hey, it worked, nothing cooks! </p> http://forums.leaflabs.com/topic.php?id=589#post-3264 Thu, 30 Dec 2010 14:06:05 +0000 gbulmer 3264@http://forums.leaflabs.com/ <p>@mikep - no harm done, and you did give an excellent answer which is what the OP needed, and anyone else who finds this thread in the future.</p> <p>Happy New Year ;-) </p> http://forums.leaflabs.com/topic.php?id=589#post-3263 Thu, 30 Dec 2010 13:17:02 +0000 mikep 3263@http://forums.leaflabs.com/ <p>@gbulmer</p> <p>I know I know :), point taken. I'm an electronics engineer by trade so I was indoctrinated using exact terminology, even though many times the real world seems to be more "fuzzy"... </p> http://forums.leaflabs.com/topic.php?id=589#post-3260 Thu, 30 Dec 2010 11:35:44 +0000 ianmga 3260@http://forums.leaflabs.com/ <p>@mikep, thanks a lot. That's what I wanted to know. I'll use the resistor. </p> http://forums.leaflabs.com/topic.php?id=589#post-3257 Thu, 30 Dec 2010 09:47:23 +0000 gbulmer 3257@http://forums.leaflabs.com/ <blockquote><p>"TTL" usually implies 5V logic, 3.3V devices usually use LVTTL</p></blockquote> <p>I try not to ASSuME too much :-)</p> <p>FTDI USB to serial cables are described as TTL, but are sold in 5V and 3V3 versions.</p> <p><a href="http://uk.farnell.com/ftdi/ttl-232r-3v3/cable-usb-to-ttl-level-seri-converter/dp/1329311" rel="nofollow">http://uk.farnell.com/ftdi/ttl-232r-3v3/cable-usb-to-ttl-level-seri-converter/dp/1329311</a> </p> http://forums.leaflabs.com/topic.php?id=589#post-3256 Thu, 30 Dec 2010 00:06:23 +0000 mikep 3256@http://forums.leaflabs.com/ <p>"TTL" usually implies 5V logic, 3.3V devices usually use LVTTL, which has lower voltage levels.<br /> Some of the STM32/Maple pins are 5V-tolerant, see here:<br /> <a href="http://leaflabs.com/docs/gpio.html#pin-mapping-mega-table" rel="nofollow">http://leaflabs.com/docs/gpio.html#pin-mapping-mega-table</a><br /> So the USART1/USART3 pins are 5v-tolerant, but USART2 pins are not!</p> <p>Even when using a 5V tolerant pin, I usually put a resistor (about 1k) into the Rx and Tx lines, just in case you hook the two Tx lines together accidentally. You should not need a voltage divider or level shifter: a voltage of &lt;0.8V equals "0" in LVTTL and in TTL. And the "1" voltage in LVTTL (&gt;2.4V) should be recognized by standard TTL as a "1" as well. Nice diagram here:<br /> <a href="http://www.interfacebus.com/voltage_LV_threshold.html" rel="nofollow">http://www.interfacebus.com/voltage_LV_threshold.html</a></p> <p> So you can hook 2 Maple's together without problems, but I would still recommend the 1k resistor for the same reason: if you accidentally connect the two Tx lines and they are both using push-pull output mode you can fry the outputs. </p> http://forums.leaflabs.com/topic.php?id=589#post-3254 Wed, 29 Dec 2010 21:59:11 +0000 gbulmer 3254@http://forums.leaflabs.com/ <p>Are both serial running at the same voltage? </p> http://forums.leaflabs.com/topic.php?id=589#post-3253 Wed, 29 Dec 2010 16:47:20 +0000 ianmga 3253@http://forums.leaflabs.com/ <p>Is it possible to connect 2 TTL serials directly or is this going to fry something? How about between two Maple's? (And of course making TX-&gt;RX / RX-&gt;TX )</p> <p> Ian </p>