SCC(4)                OpenBSD Programmer's Manual (PMAX)                SCC(4)

NAME
     scc - Zilog serial communications interface

SYNOPSIS
     scc0 at ioasic?
     scc1 at ioasic?

DESCRIPTION
     The scc driver provides support for the Zilog 8530 Serial Communications
     Controller (SCC) via the IOCTL asic on DECstation 5000 models in the
     /100, /20, and /240 series.   Each scc device has two serial ports. The
     model 20 provides one scc device.  Other models provide two, but one port
     of each device is dedicated to mouse and keyboard input, respectively.

     Input and output for each line may set to one of following baud rates;
     50, 75, 110, 134.5, 150, 300, 600, 1200, 1800, 2400, 4800, 9600, 19200,
     38400, or 57600.  Speeds up to 230400 are supported by the chip and the
     motherboard, but speeds  higher than 57600 do not work reliably without
     an external clock signal.

FILES
     /dev/ttya

     /dev/ttyb

     /dev/ttyc

     /dev/ttyd

     The mapping from units to serial-hardware  outlets is idiosyncratic.  the
     even ports are wired serial connectors and the odd-numbered ports are re-
     served for mouse and keyboard.  On machines with one port like Personal
     DECstations, the single device is ttya. On the 5000/1xx and 5000/2xx, the
     first serial port (default serial console) is ttyc and the second port is
     ttya.

HISTORY
     The scc driver first appeared in 4.4BSD.

BUGS
     The IOCTL asic provides internal DMA channels that can be programmed to
     transfer  up to 4096 bytes of data into, or out, of an SCC without fur-
     ther software intervention.  This feature of the ioctl asic is not yet
     supported.

     The mapping from device-special files (major and minor number) to chip
     and port is arguably backwards.  Ultrix tries to hide the hardware  map-
     ping, but NetBSD does not.  Users wanting to use Ultrix compatible tty
     names /dev/tty0 and /dev/tty1 for the scc comm-port lines should make
     links or device-special files which match their hardware setup.

OpenBSD 2.9                     August 6, 1996                               1
