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Before adding a modem, ensure there is a port available on your system -- either directly on the COM1 or COM2 serial ports, or on a third-party multiport card. If you are installing a supported modem, use the Modem Manager to configure an SCO OpenServer-supported serial card. Otherwise, you can use the Hardware/Kernel Manager or the mkdev serial command to add support for additional serial ports, or a vendor-supplied configuration utility for third-party intelligent serial port devices and drivers. See ``Adding serial and parallel ports'' for more information.
If you experience this problem, reboot the system and use the unix.old kernel at the boot prompt until you have corrected the situation.
For systems with two dumb (non-intelligent) single-port serial cards, /dev/tty1a and /dev/tty2a are the non-modem control devices associated with COM1 and COM2 respectively. /dev/tty1A and /dev/tty2A are the corresponding modem control devices for these ports. The operating system gives these ports different device names because it uses different device-driver routines for each.
For systems with dumb multiport serial cards, /dev/tty1a through /dev/tty1h and /dev/tty2a through /dev/tty2p are non-modem control devices, and /dev/tty1A through /dev/tty1H and /dev/tty2A through /dev/tty2P are modem control devices.
Vendors of multiport smart serial cards implement their own drivers and device naming schemes; consult the documentation supplied with your smart serial card for details.
Make sure the serial port you have chosen for your modem is recognized at bootup (check /usr/adm/messages or use hwconfig(C)) and, if the modem is internal, make sure that the interrupt vector (IRQ) and base I/O address of the COM port do not conflict with any other device.
If you attempt to use both modem and non-modem control ports at the same time you will see the warning:
cannot open: device busy
See also: