Re: rs485 on SBC84500

From: T Marchini (a.marchini_at_ohknow.com)
Date: 06/19/05 

Date: Sun, 19 Jun 2005 14:46:25 GMT

Grant Edwards wrote:
> On 2005-06-18, Frencia <jean.pierre.frencia@wanadoo.fr> wrote:
>
>
>>I'm trying to use the RS485/COM2 port on an embedded Axiom
>>SBC84500 card running kernel 2.4.26. I have configured the
>>JP9,JP10,JP10 according to the documentation but there is no
>>output signal when writing to /dev/ttyS1.
>
>
> You might have to assert RTS in order to enable the RS-485
> drivers.
>
>
>>I read somewhere that I should use ioctls to write to the port
>>instead of the standard write function.
>
>
> I really doubt that. I've been doing serial stuff under Unix
> for 15 years, and I've never heard of using ioctl() to write
> data to a serial port.
>
I have. If a sufficient driver was never created, you end up using ioctl
to control the devices registers directly from user space. It simplifies
the work of the device developer in exchange for giving the end user a
headache.
If the device doesn't have a clean "port" into the linux realm (special
non 16C550 compliance for example) then it this might be the easy way to
get a board off the ground.
T.

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