[En-Nut-Discussion] AT91 RS485

[Harald Kipp]

Coleman Brumley wrote:
> Harald,
> 
> I am also using half duplex RS485 on the AT91 platform.  However, I
> specifically set up the registers in the CPU to do this at startup -- I
> don't rely on the "USE HW RS485 on UARTx" feature.  

I read about problems with some RS485 level translators taking too long
to switch from receive to transmit or vice versa. The AT91 offers a
timeguard value for the latter, but not for switching back to transmit mode.

It's a kind of academic question because the driver will support
switching a GPIO anyway. I'm just curious if this is a real world
problem or just an urban legend. And I'm wondering why Atmel implemented
this timeguard at all. In RS485 mode the RTS status is tied to TXEMPTY,
which ensures, that the last character had been completely shifted out.

Harald