5.3.7. Serial and Parallel Ports

Nearly all systems have these. If you are attaching a printer to one of these ports, the Printing section of the handbook is very useful. If you are using modem, Dialup access provides extensive detail on serial port configuration for use with such devices.

device sio0 at isa? port ``IO_COM1'' tty irq 4 vector siointr

sio0 through sio3 are the four serial ports referred to as COM1 through COM4 in the MS-DOS world. Note that if you have an internal modem on COM4 and a serial port at COM2 you will have to change the IRQ of the modem to 2 (for obscure technical reasons IRQ 2 = IRQ 9) in order to access it from FreeBSD. If you have a multiport serial card, check the manual page for sio(4) for more information on the proper values for these lines. Some video cards (notably those based on S3 chips) use IO addresses of the form 0x*2e8, and since many cheap serial cards do not fully decode the 16-bit IO address space, they clash with these cards, making the COM4 port practically unavailable.

Each serial port is required to have a unique IRQ (unless you are using one of the multiport cards where shared interrupts are supported), so the default IRQs for COM3 and COM4 cannot be used.

device lpt0 at isa? port? tty irq 7 vector lptintr

lpt0 through lpt2 are the three printer ports you could conceivably have. Most people just have one, though, so feel free to comment out the other two lines if you do not have them.