Adding serial and parallel ports

Troubleshooting serial cards

Older computers or add-on serial I/O cards use the slower 8250 or 16450 UARTs to control their serial ports. Some revisions of the 8250A chip do not handle interrupts properly and should not be used with SCO OpenServer systems.

Problems with slow UARTs can show up when using UUCP or cu(C) over a modem connection at high line speeds. Examples are:

incoming characters are lost intermittently
UUCP generates unkillable uucico processes
cu stops executing and will not exit
an intermittent ``double echo'' is seen

These problems rarely show up when a serial port is used with a terminal. They are more often associated with high-speed serial input over a modem link. Avoid connecting high-speed modems to ports that are controlled by slow serial control hardware such as 8250 or 16450 UARTs.

NOTE: We strongly recommend that you use 16550 (or better) UARTs on serial ports that are connected to high-speed modems. The 16550 has a 16-byte receive buffer that allows it to operate reliably at much higher speeds than the 8250 and 16450 (see ``Serial port speeds, line-mode labels, and UART limitations'').

See ``Serial device resources'' for information about how to monitor and tune the performance of dumb serial ports.