RE: [uCsimm] Problems with RTS and CTS in uCsimm

From: Asier Goikoetxea Yanci (
Date: Fri Jan 05 2001 - 10:54:41 EST

        Hello Vladimir,

>CTS/RTS signals are used for flow control on RS-232. I.e if you
>send too much data to the modem, it will de-assert CTS and re-assert
>it after it frees up some of its internal buffers. If your system is
>too slow and the modem receives too much data from the outside, uCsimm
>might de-assert RTS so that the modem could then apply backpressure to
>the far end.
>From your description I don't think you have any flowcontrol problems,
>thus it probably has nothing to do with CTS/RTS.

I have disabled flowcontrol on modem settings.

>> 2.-I use telnet as a login, i don't use ttyS0 because i have
>> a modem in, and i have changed /etc/inittab file for not use ttyS0 as
>> 3.-I type agetty -w -I 'AT\015' 9600 ttyS0 to start the modem
>> connected on port ttyS0.
>Well, first of all, agetty is supposed to run only ONCE. It should
>be respawned afterwards. That's why it is in /etc/inittab.

I know, but I execute agetty from telnet because it's more confortable for
me at the moment.

>Second, make sure, your modem is configured in such a way that it does not
>echo the AT commands.


>Third, and most important. To be able to support dialin modem connections
>you have to have DCD pin on your RS-232, but M68EZ328 UART does not provide
>it. This should cause some problems with agetty. E.g. if you configure the
>modem as I told you before, you'll probably need to hit <return> after
>connect and then you'll get "Password: " prompt instead of "login: "
>and stuff like that.

Well, if I connect uCsimm's ttyS0 port to a PC, and execute agetty command
from telnet in uCsimm (agetty -w -I 'AT\015' 9600 ttyS0), I can see in the
minicom, in the PC, AT string and after that starts the login. It seems that
works. But if I connect uCsimm's ttyS0 port to a modem and type de same
command from telnet, it do the same as connectting to the PC, I mean, the
modem will recive AT command, but it doesn´t inicialize, so I cannot connect
to uCsimm via modem. I have disabled DCD, DSR, DTR, RTS and CTS. I only use
to RxD, Txd and GND to comunicate the uCsimm whith the modem. Wath am I
doing wrong?

>Alternatively, you should use a much more sophisticated getty, like mgetty,
>which does not rely on the RS-232 I/O being blocked until DCD is asserted.
>But you'll need to port it yourself.

Thanks in advance

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