[lkml]   [2003]   [Mar]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRE: RS485 communicatio
On Wed, Mar 12, 2003 at 10:15 PM, wrote:
> Hi all,
> am currently working on PPP over serial interface (RS485) in
> linux 2.4.2-2. I believe RS485 half duplex system and hence
> only one can transmit at a time. And for RS485 we basicaly
> use Master-Slave or Primary-Secondary kind of communication.
> I don't know how to achieve the same using PPP since i need
> to have max of 10 nodes connected via serial interface. I
> tested with two nodes using PPP daemon it works fine.
> Following are the commands i issued
> In PPP server:
> $usr/sbin/pppd -detach crtscts
> 115200 /dev/ttyS0 &
> In PPP client side :
> $/usr/sbin/pppd call ppp-start
> where ppp-start file is copied into directory /etc/ppp/peers/
> that had the following
> -detach /dev/ttyS0 115200 crtscts
> noauth
> This point to point communication worked fine with RS485
> interface. If i had to connect one more node what i need to
> do. Please clarify with the following
> i) Whether the existing pppd takes care of the RS485 with
> multi node , if so how do i manage giving commands
> ii) If there is no direct support how do i go ahead. Is there
> any other layer 2 protocol allows me to acheive TCP/IP
> communicattion over RS485 which is my ultimatum.
> I will be grateful if anybody of them could help me with my
> current problem.

I believe Point-to-Point Protocol only supports point-to-point symmetric
links. Don't think there is any multi-point support in the protocol. IIRC,
PPP also requires a full duplex link, which is not available on an RS-485
link with more than two stations, even if it is a 4-wire link.

I don't know of an easy way around this fundamental limitation.

Maybe somebody on the kernel list has a suggestion.


Ed Vance edv (at) macrolink (dot) com
Macrolink, Inc. 1500 N. Kellogg Dr Anaheim, CA 92807
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2005-03-22 13:33    [W:0.078 / U:0.604 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site