Hi guys,
Some feedback from Jerome about new Jaluino Medium v2.0 design brought to me some thoughts I'd like to share. This is about serial connector pinout. I had also discussed this with Richard and Rob, here's a summary. Goal is to provide a serial connector compatible with FTDI cable. Cable pinout looks like this: [image: ftdi.png] Datasheet says: - TXD is output - RXD is input - CTS is input - RTS is output (so labels on cable side really correspond to functions it exposes, and not the function that should be connected). Currently, Jaluino v2.0 design provides the following serial connector: [image: v2.png] Labels RTS and CTS are wrong, but this is just a detail... The question is: does this serial connector pinout is compatible with FTDI cable's ? To make proper compatible serial connector, I'd say we need to swap signals, as: - TXD goes to RXD - RXD goes to TXD - CTS goes to RTS - RTS goes to CTS but there seems to be discussion about RTS and CTS signals. Some would like to cross signals, just as RX and TX, some wouldn't. The question is related to how a PIC and a PC acts. DCE ? DTE ? Historically, modems were declared as DCE, and were connected to PC using straight cable (not even RX/TX cross-over). When connecting two DTE equiments together, a cross-over cable is used (null modem), where RX/TX signals are crossed, and the same for RTS/CTS: - RX(PIC) <- TX(PC) - TX(PIC) -> RX(PC) - RTS(PIC) -> CTS(PC) - CTS(PIC) <- RTS(PC) (where arrows mean "output -> input" and "input <- output") This means, whatever side, CTS is an input, RTS is an output. But looking at serial_hw_int_cts.jal library, CTS must be declared as output. This is because (Rob, correct me if I'm wrong) using this lib expects both CTS lines are connected together (no cross-over). Whereas RX/TX signals are crossed. So there's a kind of a mix between a straight and a cross-over cable. Where is the standard ? Where is the truth ? According to me, we're in DTE-DTE communication, when you start crossing signals with RX/TX, you should then cross all signals to match a standard null-modem cable used in such configuration. This means, to be compatible with FTDI cable's pinout, there's a mistake in RTS/CTS signals in Jaluino's serial connector (RTS and CTS must be swapped). But this would also mean there's something wrong in serial_hw_int_cts library, as CTS really should be an input and be connected to RTS on the other side. If you're still there, do you have any suggestions, comments, ... ? PS: if you think there's a typo, please tell me ! :) TIA Cheers, Seb Cc: jaluino, jallib groups 2010/10/13 Sebastien Lelong <[email protected]> > Hi guys, > > Richard has designed our new Jaluino Medium board, v2.0. In SVN you'll find > schematic, PCB, Gerber files. Several improvements were requested ( > http://code.google.com/p/jaluino/issues/detail?id=25), this new version > fixes many of them: > > - onboard LED, with jumper selection > - several fuse options so everybody's happy (none, pico fuse, or "big" > fuse as before) > - more space near 7805 voltage regulator to add a cooler > - selection power for the whole board, with 3V3 or 5V (though we still > have doubts if USB will work at 3V3...) > - labeling has been improved for better reading and identification > - serial connector pinout has been changed to map standard FTDI cable > (this means v2.0 isn't compatible with previous version on this point, > careful when plugin your serial adapter) > - double-sided design, no more vias > > And, since availability was also mentioned as an important improvement, I > plan to order 10 pcs very soon (actually 8 available), as a new batch order. > Since this hasn't been built for real before, please consider this batch > order as *beta*: it may not work, it may not be perfect, some tinkering may > be required, etc... If you don't want to take the risk, please keep yourself > away (but not too much :)), a man forewarned, a man forearmed... And most > importantly, for this to be a success, better have lots of eyes than just > few (can't remember the proverb...). Can you give a look at this and, maybe, > point some potential problems ? > > All files can be found here: > http://code.google.com/p/jaluino/source/browse/?r=256#svn/trunk/mainboard, > name "v20". I can provide image for top/bottom gerber files if you like. > > > Thanks to Richard for his work, and thanks in advance for your feedback. > > Cheers, > Seb > -- Sébastien Lelong http://www.sirloon.net http://sirbot.org -- You received this message because you are subscribed to the Google Groups "jallib" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/jallib?hl=en.
<<v2.png>>
<<ftdi.png>>
