Re: [Gumstix-users] rs232? woes

[Peter D. <pda...@pc...>]

Miguel,

Thanks for the response  --it would appear that you're right. I switched 
tx/rx, so it must be my serial command procedure (echoing ascii values at 
command-line, which worked from my winblows box).  If you would post the 
code you used, I would be ecstatic.

-Peter

On 5/10/05, Miguel Piedrahita <mi...@st...> wrote:
> Peter,
> I recently interfaced a gumstix with a MotorMind B, and I used a chip
> similar to a MAX232 to shift the voltage levels.  I think the gumstix puts
> out the exact same RS232 voltages that your PC does, so if it works from
> your PC you should be ok in that respect.
> One thing to check is whether you're using the correct Tx, Rx, and ground
> pins from the gumstix serial port.  It's easy to mess this up, as it
> depends on the cable you're using (i.e. null-modem or not).  Pinouts are
> posted on the TikiWiki under Hardware -> IO.
> Another possible issue is that the MotorMind B is pretty sensitive to
> the timing of the serial commands you send.  It's not explained
> anywhere in the data sheet, but I found that if the bytes in a command
> are spaced too far apart then it doesn't work.  So depending on how
> you're sending the commands from the Gumstix this could be the
> problem.  If that's the case let me know and I can post the code that
> worked for me.
>
>  - Miguel
>
> >
> > Like mr hylands, gumstix-users posts would not go through from gmail,
> > sorry
> > if this message is duplicated.
> >
> > Hokay,
> >
> > I am still working on communication from the gumstix serial port to a
> > motor control unit (solutions cubed's motormind b).  Pardon my
> > ignorance and the barrage of questions...
> >
> > I successfully have the MMb working via a MAX233a IC, talking to my
> > pc's 11v RS232, but no dice on the gumstix. The max233a turns TTL or
> > CMOS (up to 5v) into RS232 for standard PC serial-port communication.
> >
> > I've read that the gumstix has a 3.3v logic level (TTL? CMOS? swing
> > voltage of..?) for the externally interfaced minidin8, right? Then why
> > do I read 5v? And how does ttyS0 talk to my PC's 11v if it's 3.3v ?
> > Doesn't that tell me that I should be able to use the same MAX233A
> > chip to talk to ttyS0, since my PC can communicate to/from ttyS0?  But
> > that does not work, nor did I cook it from trying..
> >
> > I don't really understand what logic family the gumstix is using.
> > Maybe the voltages & voltage swing are where my problem lies. I will
> > try to give enough information for somebody to help out.
> >
> > The motormindb is powered with a regulated 5.0v. So this becomes my
> > Vcc constant.
> >
> > According to the documentation, the MMb accepts serial asynchronous
> > communication with a swing of :
> >
> > Input Low:    GND(min)  to .2Vcc (max)   ( I interpret that as -5v to
> > 1v being an acceptable 'low') ?
> > Input High:   2.0  .2Vcc+1V(min)  to Vcc(max)   ( 2v to 5v as an
> > acceptable 'high') ?
> >
> > That's verbatim from the DC characteristics chart.  I may need some
> > help on the interpretation of those voltages & swing, but the output
> > is straightforward:
> >
> > Output Low:  .6V
> > Output High:  Vcc
> >
> > Again, pardon my ignorance.  If anyone can give me some pointers for
> > communication or answer any of my questions, I would be eternally
> > grateful.
> >
> > -Peter
> >
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