The confusion I am trying to clear is that more than one driver on an
RS-232 line will not work properly and will result in erroneous data.
Multiple receivers are no problem.
Besides, you are quoting the standard for the receiver input. In order
to drive the long lines (as originally intended for RS-232), the driver
output must be much greater. Capacitance in the cable and resistance
can distort the waveform and reduce the voltage. Not usually a problem
with short lines encountered in typical PC and ham radio setups, but is
problematic when the line length gets long.
There is a difference between "it works", and "it works right all the time".
73,
Don W3FPR
On 9/15/2014 11:15 AM, Lynn W. Taylor, WB6UUT wrote:
There is the formal standard, and there is the defacto standard.
The formal standard says +3v for 1, -3v for 0, and that less than 3v
is undefined.
The common driver chips (1488 and 1489) worked just fine with TTL
levels -- 5v being above +3, and 0v being close enough to -3v.
I've never seen anything that required -3v for logic zero.
-- Lynn
On 9/15/2014 6:59 AM, Don Wilhelm wrote:
David,
That is true the specification says that condition will not cause
damage to compliant drivers and receivers, but if two drivers are
placed on an RS-232 signal line, they will *not* work together and
will result in corrupt data (assuming they are on the TXD or RXD
signal lines).
You are correct that damage may occur to non-compliant (but
compatible) drivers and receivers. The PC serial cards, USB to
serial adapters, and most ham gear do not implement compliant RS-232
interfaces.
73,
Don W3FPR
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