seria port communication on linux with rts signal

seria port communication on linux with rts signal

[Ravi]

Dear All,

I want to interface a printer on RS232 port of my arm board.the printer has
RX,TX and CTS signals from printer. This pin will turn to logic low indicating
printer is ready to receive data. If Printer is not ready to print then the
signal will
change to Logic High. I have interfaced null modem communication on serial
port.can any one let me know the changes to accommodate CTS signal interrupt
from printer.

Thanks & Regards,
Ratheendran

seria port communication on linux with rts signal

[Russell King - ARM Linux]

On Mon, Jul 18, 2011 at 09:44:13AM +0000, Ravi wrote:
> Dear All,
> 
> I want to interface a printer on RS232 port of my arm board.the printer has
> RX,TX and CTS signals from printer. This pin will turn to logic low indicating
> printer is ready to receive data. If Printer is not ready to print then the
> signal will change to Logic High.

Your description is confusing.

RS232 is not logic levels.  RS232 is positive and negative voltage
signalling.  A logic 0 coming out of the serial port is converted to
a positive voltage, a logic 1 is converted to a negative voltage.

The RX and TX logic signals into/outof the RS232 driver are positive
logic (a '1' bit is logic 1) and on the RS232 connector that's a
negative voltage.

The CTS logic signal will be inverted (so /CTS) and its active state
will be logic 0, meaning 'clear to send'.  On the RS232 connector,
this will be a positive voltage.

Assuming that the above is what you meant, this is standard signalling,
and your UART should already be able to cope with this in hard flow
control mode - it will send characters when /CTS is logic 0, and hold
off sending characters (which can still be queued in the kernel) when
/CTS is logic 1.

If you don't know how to control the flow control method, you need to
read up on stty, termios, and specifically the CRTSCTS flag.