Not control chars after all...
A fractured saying I sometimes use is "if it's not one thing, it's two things." It's hard enough to track down one problem, but two problems can increase the difficulty expotentially.
Here was my 422 test network: PLC-indexer1-indexer2-422/232card-laptop(running hyperterm)
Here was my 2 things problem
Thing one: PLC output would not appear on laptop unitl I wired it to the network "backwards". Everthing else was wired TX+ to TX+, TX- to TX-, RX+ to RX+ and RX_ to RX-. But the laptop had to be TX+ to RX+, TX- to RX-, and so on, to be visible on hyperterminal. So I figured that must be right. But the indexers didn't react to PLC commands.
Thing two: in the 2 day process of trying every possible combo, I hooked up the PLC the "normal" way, TX+ to TX+, etc. But still the indexers got nuthin'.
Solution: Several times I tried the network with the 422/232 interface card (FA-ISONET) removed, but no luck. But today I removed the inteface card and ACCIDENTLY hooked up the PLC the "normal" way and it works!
So just by luck I discovered my 2 problems.
One (minor): PLC can't be seen on hyperterminal through interface card when hooked up correctly for indexers.
Two (biggie): indexers can't recieve from PLC when interface card is on the network. For some reason the card hold the transmit line high all the time, apparently preventing another device from controlling the line.
Not very elegant, but I thought I'd document my solution for posterity. Thanks Eric for your help.