Tested the cable; no probs.  It's a 7-wire serial "null-modem" cable;
2->3, 4->5, 6->20 and 7->7...
so my computer and vt100 are both DTE's... no prob...
they both assert RTS, TxD, and DTR... but nothing happens..
I figure it's because of DCD, so I set clocal on the line in /etc/ttys
and kill -s HUP 1.... still no dice..

Do I really need a wire shorting DCD and DSR together, or is there a
simpler way?