Re: [LI] Modem problems

[Bhyrava Prasad <prasadb@xxxxxxxxxx>]

Vaibhav Patkar wrote:
> 
> Dear Amol
> 
> Normally a mother boards gets +5V, -5V, +12V, -12V supply from the SMPS. It
> could happen that these voltages are not fully achieved i.e you may get +10V
> or -9V. Now it depends on the OS to recognize wheather it is Logic high or
> Logic low condition for the interface to work. Normally serial port works
> with +12V and -12V. It is possible that the SMPS is not giving proper -12V.
> Assuming it is -10V though Windows recognizes it as proper com port but
> Linux does not. The problem cannot be with +12V as your CDROM drive, Hard
> disk drives works ok.

Huh? The OS has nothing to do with recognising logic highs
and lows. The RS 232 standard says it the voltage levels should
be between 5 V to 15 V (positive for logic low and negative
for logic high). Level conversion is part of the hardware
and not of OS or any s.w!

- B. Prasad
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