oddball televideo problem

From: der Mouse <mouse_at_Rodents.Montreal.QC.CA>
Date: Thu Jan 15 12:52:54 2004

> I've had problems in the past with voltage levels on RS-232.

> One device runs -12/+12V, the other 0/+5V, and they refused to talk
> bi-directionally. Putting in a homemade level shifter (forced the
> 0/+5 to -9/+9) made it work.

I think a sending device is required to swing at least below -3V and
above +3V for it to be RS-232 (though I may have the voltages wrong,
it's been a while - but I'm sure they're symmetric about 0). I ran
into this when connecting Sun keyboards to vanilla serial ports - I
found I needed a level shifter and an inverter (of course, the inverter
may be unnecessary depending on whether the level shifter you use
inverts or not). (Sun keyboards are RS-232 except for the voltage
levels in question, and possibly impedances.)

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Received on Thu Jan 15 2004 - 12:52:54 GMT