[time-nuts] RS 232

[David McGaw]

For short cable and non-critical use, CMOS levels (0-5V) work fine. 
RS-232 receiver thresholds are actually similar to TTL levels 
(0.8-2.7V), though the spec is for +/-3V minimum drive for noise 
immunity.  Phantom power can be gotten from the control lines - this is 
how serial mice are powered.

David


On 7/25/13 10:21 AM, paul swed wrote:
> Debating the band belive ideal for older is +-3V. But I would need to
> check. And how old is old? Not to sure many of the old 1488 1489 devices
> are around anymore.
> I think more compatibility would be supported by the +-1.4 you mention.
> Regards
> Paul
> WB8TSL
>
>
> On Thu, Jul 25, 2013 at 9:39 AM, <EWKehren at aol.com> wrote:
>
>> Since joining time nuts over four years ago I have not used a  single MAX
>> 232 chip. Two reasons MAX do not give me isolation and do generate  noise
>> in
>> critical applications. I prefer the use of two H11 opto couplers which
>>   work
>> perfect. On the receiving end the diode along with a current limiter and
>> blocking diode for the negative level works perfect. On the output side a
>> power  source is needed. If one uses an USB adapter it does have the + 5
>> volt
>> which  again works perfect.  How ever many prefer to use RS 232 direct and
>> that is  why I hope to get some comments and suggestions from the list.
>> Corby
>> used on our  counter circuit that he described a separate power source.
>> Present MAX circuits use a + 1.4 volt threshold but  considering legacy the
>> question is what should the voltage swing be to make it  compatible for
>> most PC's and what options exist to get the necessary voltage. In  the past
>> other pins on the RS 232 port where an ideal power source. Still an
>>   option?
>> Bert Kehren
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