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Re: RS485 9-bit networking




----- Original Message ----- 
From: Bart Duchesne <bduc@xxxxxxx.com>
To: <dev-etrax@xxxxxxx.com>
Sent: Monday, May 07, 2001 10:04 AM
Subject: RS485 9-bit networking


> Hi guys,
> I have a few simple questions regarding serial transmission.
> 
> Can the etrax use 9-bit data transmissions on its RS485 serial port.

There is no 9-bit mode, but by using 8 bit+parity you can acceive 
9bit without parity.
This is fairly straight forward for sending, although you might want
to use interrupt driven I/O instead of the DMA (depending on how 
often you need to change the ninth bit)
When receiving, you could check the parity error to make an 
educated guess about what the ninth bit really was.
Using char-by-char interrupts instead of DMA is probably a good idea here.

> Are there any documents regarding the registers and settings of the 
> serial ports or do I have to dive into the kernel source.
> (parallel ports seem to be desacribed in detail, but the serial docs I 
> can't find anywhere)

All documentation for ETRAX100LX is not reviewed yet and is 
therefor not published on developer.axis.com yet, 
you can look at the ETRAX100 documentation for now. 
Check out ETRAX 100 Designers Reference, Register Definitions.


> I want to write my own serial RS485 9bit 'network' driver for the 2.4 LX 
> kernel to interface it to a RS485 network of atmel microcontrollers.
> Is there anybody out there who has started something like this ?

I know that we have had questions about 9-bit RS-485, but I don't
know if someone has started working on it.
 
> regards,
> 
> bduc@xxxxxxx.com

/Johan