> If you just want to use [rts/cts] for flow control there shouldn't
> be any problems...

Assuming YOUR idea of "flow control" matches the USB vendor's idea of
"flow control."  I wouldn't expect "standard" half-duplex flow control
(ie RTS/CTS as defined in the rs232 specifications, which is quite
different from how it's generally used these days) to work through
any USB serial adaptor, or even the windows serial APIs, for example.

> I can set RTS to tell when a complete data was sent and
> cts when complete data is received
>
Is that what you meant?  That's unusual even by the bent standards of
todays usage.

Modern usage: CTS (input) will be "true" when the other side has room
   for you to transmit additional data.  RTS (output) is set "true" when
   you have room to receive data.  Usually handled by hardware to acheive
   FIFO-level flow control.

Traditional (half duplex) usage: RTS (output) is set "true" when there
    is data to transmit.  CTS (input) will be "true" when the modem has
    successfully switched direction and you can transmit.  RTS is set
    "false" when data transmission is done.

DTR, DSR, CD, and RING would normally be involved only at "call setup
time" for both modern and traditional usage:

Traditional:
   The modem detects the phone ringing and blips RING.  the computer
   notices and asserts DTR, which causes the phone to answer.  The modem
   trains and asserts CD and/or DSR, and the computer responds by
   starting a session.  To end call, computer drops DTR or modem drops
   CD/DSR (and computer responds by dropping DTR.)  DTR is off in idle.
   (I don't recall the distinction between CD and DSR.)

Modern:
    Modem detects phone ringing, answers phone, and trains up all by
    itself, then asserts DSR or CD, which the computer notices and
    starts a session.  Session is ended by computer dropping DTR or
    modem dropping DSR/CD.  DTR is ON in idle; typically the modem
    will not answer calls unless DTR is ON.  (backward compatibility
    is achieved by blipping RING during ring regardless, at which time
    the computer can assert DTR, which allows the modem to auto-answer.)

You can confuse yourself by trying to think of voltage levels instead
of logical states; there are a couple places where voltage inversions
occur.  Thus the ambiguity of "assert" and "true" in the above...

If you're going to fiddle with rs232, you should build or buy
yourself a dual state (two colors of LED per lead) rs232 breakout or
monitor box.  Alas, db9 is the modern standard for rs232 connectors,
and db9 monitors seem rather uncommon; I have a cute double-sided
EAGLE PCB that works pretty well, if anyone is interested...

BillW
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