[SML] strange RS-485

[Jerry Durand]

I thought I'd seen some tricks, but this one rates high on the
"interesting" level.

Standard MAX485 chip BUT, the /RE and DE lines are driven by the TX
data.  On the RS-485 side there's an active termination that pulls the
line to marking.  So a space on the TX data enables the transmitter and
drives the RS-485 to space.  A mark disables the driver so the
termination pulls it back to marking time.

The receive data then is only active while the TX line is mark.

Half duplex data without complicated switching.

Personally I would have put a slight delay (maybe an RC network) between
sending the Mark so the RS-485 chip would drive it, and THEN I would
remove the enable.

-- 
Jerry Durand, Durand Interstellar, Inc.  www.interstellar.com
tel: +1 408 356-3886, USA toll free: 1 866 356-3886

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