Path: utzoo!mnetor!tmsoft!torsqnt!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!zaphod.mps.ohio-state.edu!rpi!uupsi!sunic!kth.se!news
From: wahlsten@elixir.lne.kth.se (Torbjvrn Wahlsten)
Newsgroups: comp.os.minix
Subject: Re: PC Minix Serial Ports
Message-ID: <1991Feb11.001739.28001@kth.se>
Date: 11 Feb 91 00:17:39 GMT
References: <10561@bunny.GTE.COM> <1991Feb10.095318.6603@nuchat.sccsi.com>
Sender: Jorgen Wahlsten
Organization: Dept. of EE, Royal Institute of Technology, Stockholm, Sweden
Lines: 25

In article <1991Feb10.095318.6603@nuchat.sccsi.com> kevin@nuchat.sccsi.com (Kevin Brown) writes:
>... Anyone know how
>to do DCD detection on the IBM rs232 ports?  The only modem status bit defined
>in the serial driver is CTS (0x10).  Could someone post a complete listing
>of the modem status bits in the serial port's status register?

I've seen the problem before, but i've never tried to connect a modem to
Minix myself.

In either case, the modem-status bits are (b7 -> b4) DCD, RI, DSR, and CTS.
(Please, note that they are all active high).
Bits 3 to 0 are the delta-values (state-change) of the bits 7 to 4. Each
delta-bit will be set whenever a change is noted in the corresponding
status-bit (e.g. DCD: Bit 3 (Delta) corresponds to b7 (Status)).
The only exception is b2 (RI-Delta) which is set only whenever RI goes
from high to low state.

If Minix is already catching interrupts when CTS is changing state,
you will only need to add code to see wheter it was CTS or DCD that
caused the interrupt.

Good Luck!

/Jorgen Wahlsten
wahlsten@lne.kth.se