#10 RS485 Mode Invertion Option

open
nobody
Comm (5)
5
2013-01-13
2003-08-25
Ray Abram
No

The hardware that I am using to control the RS485 bus
has the RTS Control the opposite way around to how it
is currently controlled

Currently
Tx = Raised
Rx = Lowered

My Hardware
Tx = Lowered
Rx = Raised

Feature Requested:
A User controllable flag to control the direction control
logic
eg: RS485DirMode which can be set to
RaiseToTx (how it is currently)
LoweredToTx (how i need it to be)

NOTE:
I have built the hardware this way to more closely
reflect how the Actual RS485 driver chip works (sipex
3485CN) works, thus reducing the electronics and thus
the price of the adapter

Discussion

  • Logged In: YES
    user_id=70306

    Hello,

    when I read your demand, I remembered the work at my last
    company with such a feature. To say it simple: forget about
    it. The change of the RTS/CTS signal is inherited from the first
    RS232<->RS485 converter available and many producers of
    converter hardware made it "hardware compatible" to that
    thing (a huge iron block). The Win32 driver allows for semi
    duplex data transfer, but only with the correct RS232 flanks.
    There is an API event to control the RTS signal directly, but
    the flush signal, when the last character is sent to the
    converter is coming asynchronous, so for most protocols the
    manual API flow control is much too slow and unreliable (
    after installing the Win 98 plus! packet, fast mouse
    movements crashed communication, for example) . We tried
    to access the serial hardware directly, as the standard
    chip (16550?) is generating an interrupt when all chars are
    sent, but capitulated when we found out that modern laptops
    do not try to emulate the old separate serial chips but deliver
    their own Windows software driver for their proprietary
    hardware. We spent man months on that only to find it
    be a dead end. Much easier to add a not gate to your
    hardware.

    Best regards

    Dietmar