Here's what my hardware guy says; hope it's what you
were looking for.
..Stu
> > > Can someone help me with coming up with a generic, orthoganal set of
> > > ways in which half-duplex connections can differ (i.e., which RS-232
> > > line to use, delays before transmission, delays after transmission,
> > > etc.) that cover all of the different, incompatible ways that
> > > half-duplex is done? If we can do that, we can use a bitmask to
> > > describe all of the different ways that half-duplex can be done.
>
> - RS-232 does not apply.
> - In terms of our hardware the delay is fixed and NOT user adjustable
> - In terms of implementation, half duplex can be achieved totally in
> hardware, or a combo of software and hardware.
> - The actual hardware implementation will differ from one manufacturer to
> another, I guarantee it!!
> - In some cases the RTS and/or DTR signals are used to enable/disable
> (tr-state) the RS-485 transmitter. The RTS/DTr is controlled by software
or
> the driver.
> - In other cases it is implemented in hardware like CTI. Note that some
> manufacturers hardware uses jumpers and dip switches to enable the 1/2
> duplex, where as we have a software interface to enable this mode.
> - To enable 1/2 duplex on a CTI board it is only a matter of
> setting/clearing a few bits in some registers here and there. From then on
> it is entirely transparent to the **driver** and the user.
>
> To sum up the ways 1/2 d can be done...
>
> 1 - Software and hardware using RTS/DTR, application toggles RTS/DTR
> 2 - Driver and hardware using RTS/DTR, driver monitors TX fifo. When it is
> empty,and no more chars a queued to go, then change state of RTS or DTR.
> Driver must also ignore/throw away RX-ed chars while you are transmitting
> ( remember that in 1/2 D the tx is tied to the rx )
> 3 - Total hardware solution like CTI, where the board is "set-up" via
> software and the rest is entirley transparent to the driver/user
>
> Hope this helps
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