Re: RS485 implementation questions (primarly in atmel_serial.c)

[Grant Edwards <grant.b.edwards@gmail.com>]

On 2013-01-23, Guido Classen <clagix@gmail.com> wrote:

> I this cases you need a way to assert RTS some milliseconds before the
> first character of a frame is transmitted and leave it on some
> milliseconds after the end of the frame. In my opinion that is what
> delay_rts_before/after_send should be for. (In other equipment this
> feature is also called turn on / turn off delay)

In applications like links using half-duplex modems, you may have to
assert RTS for many hundreds of millisconds to allow the modulator to
key up and stabilze and the demodulator to lock onto the signal before
you can send data.  Some modems will let you know when they're ready
by asserting CTS, and for others you just have to have a fixed delay.
In those cases, you also typically hold RTS for some time after the
end of the data for a time ranging up to several byte times.

In our non-Linux based products, we implement pre/pose data RTS "hold"
times as you describe in our device driver.  Our Linux-based products
can't handle those applications.

-- 
Grant Edwards               grant.b.edwards        Yow! Are we laid back yet?
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