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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