Most 4WE&M muxes have at least two signaling configurations, usually described
as Type 1 and Type 5. More elaborate cards may also have Type's 2-4. They
describe various combinations of battery or ground on M, to idle or activate,
and battery, open, or ground on the E lead when idle or active.
What you want to look for is the configuration for type 5 signalling. This is
battery on the M lead (-24 or -48) that gets pulled to ground to send M lead.
The E lead floats open until active, then pulls to ground when active.
That combination is the easiest to deal with, but still requires care on the M
lead. An opto isolator is the made-to-order solution.
Mel - WA6JBD
