11 Feb
2006
11 Feb
'06
4:05 p.m.
On 2/11/2006 at 4:46 PM Richard wrote:
Speaking of current loop interfaces, just exactly how
is data
transmitted? Is it a current pulse train?
It's exactly what it sounds like. Instead of a voltage driven signalling
as RS-232C, the current loop interface is driven with a current source
(20ma or the older 60ma) for space and the signal is interrupted (no
current) for mark. The big advantage is that so long as the specified
current is maintained, the distance between the sender and receiver can be
substantial. In the old days, the selector magnet on a teletype would be
part of that circuit. IIRC, this is also where the name for the "break"
key came from--it interrupts the circuit.
Cheers,
Chuck