sales[at]netexpresslabs[dot]com, Silicon Valley, California

Home Page

Contact and OrderInformation


See also: our serial products

Technical Information

Note that Winmodems and HSP (aka HCF) modems are not supported by Linux. If you want to use a modem with Linux you must use a "hardware modem."

ISA modems are being discontinued in favor of PCI modems. Our favorite PCI modem for Linux is the 3COM (USR) 56K PCI modem part number 2976 using the 3COM/TI chip set. PCI Modems using the  Lucent Technologies Microelectronics Group - V.90/K56flex Modem Chip Set such as the Actiontec PCI modems (PCI56012 aka IBM 33L4618) and the Multitech MT5634ZPX-PCI PCI modems are also supported by Linux. For more information see these three links: Link1, Link2, and Link3.

After physically installing your PCI modem enter your CMOS setup and disable COM2 (Serial Port 2). Boot into Linux and log in as root. Then run:

cat /proc/pci

Look at the output and locate the "bus" entry for your modem. You need to locate the IRQ and the base I/O address for the modem. Here is an example of the modem output:

	Non-prefetchable 32 bit memory at 0x00000000.

Bus 0, device 17, function 0:
    Communication controller: Unknown vendor Unknown device (rev 0).
        Vendor id=11c1.  Device id=480.
        Medium devsel.   Fast back-to-back capable.  IRQ 3.  Master Capable.
No bursts.
            Min Gnt=252.Max Lat=14
         Non-prefetchable 32 bit memory at 0xe4000000.
         I/O at 0xb800 [0xb801]

Note in the output above the IRQ is 3 and the base I/O is 0xb800. This is common for a 3COM 56K PCI modem on an ASUS board with COM2 disabled. Now link the modem to COM2 (/dev/ttyS1):

ln -s /dev/ttyS1 /dev/modem

Add this line to your /etc/rc.d/rc.local file using the IRQ and base I/O address:

setserial /dev/modem uart 16550A port 0x6400 irq 11

Then run rc.local:

. /etc/rc.d/rc.local

You can test your modem by running "minicom" at the command prompt. For example type ATDT5551212 to dial the phone number 555-1212. The modem should dial this number. "CTRL-A Q" will quit minicom.

Many new ATX mother boards feature Advanced Power Management (APM). Some implementations of APM allow the system to go into a power saving soft-off or "sleep" mode after a period of inactivity. The computer may be awaken by mouse movement, keyboard click, a specific preset system clock time or an external modem ring. For the latter to work you must use and external modem connected to the serial port. You can not use an internal modem because internal modems will go to sleep too and will not respond to a ring. Also note that these APM features only work with ATX systems, not older AT systems which lack the +5Vsb and PS-ON leads required for software mediated power control.

Copyright (c) 1989 - 2008 Net Express All Rights Reserved.