Re: serial device on ubuntu lucid lynx; update

[Johan L. <joh...@ap...>]

lör 2010-07-17 klockan 10:06 +0200 skrev Christoph Bartelmus:
> Hi!
> 
> Johan Lans "joh...@ap..." wrote:
> [...]
> > Now I have been troubleshooting for a couple of days and I have tried to
> > eliminate any possible error source. So now I'm down to this:
> >  *I've checked both serial ports with a loopback test on pins 2 and 3,
> > so now I know which port is which and that both ports are functional
> >  *I've connected my receiver, an IRM-3638N3 from Everlight, to the 5
> > volt and ground of my computer. The out-led of the receiver is connected
> > to the first pin on the serial port.
> >  *Supply voltage is measured to 5 volts on Vcc-led. Voltage on first pin
> > is about 1 volt.
> 
> That cannot work. The IRM-3638N3 output is active low and most likely  
> open-collector, but I don't see any hint in the datasheet. You need the  
> pull-up resistor at DCD to Vcc. In idle the voltage at DCD should be  
> around Vcc and go to < 1V when a signal is received. You will only see a  
> slight drop of voltage (I guess around 1V down) with a simple voltmeter.
> 
> Christoph
> 
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Super! When knowing what to look for I could pretty easily locate my
error (on the original build, not only connecting the receiver) to the
resistor (had 47k instead of 4.7k, big doh). Now I'm getting active low
detected and pulses on mode2, the rest should be easy...
 Thanks a lot (to Dave aswell). Now I know what a pull up resistor is. I
thought the resistor was part of the RC-filter seen in the data sheet...

/Johan