NAME
scc —
Zilog 8530 Serial Communications
Controller interface
SYNOPSIS
scc* at ioasic? offset ?
DESCRIPTION
The
scc driver provides support for the Zilog 8530 Serial
Communications Controller (SCC) via the IOASIC found on DECstation 5000 models
in the /100, /20, and /240 series (supported by
NetBSD/pmax).
Each SCC device has two serial ports. The DECstation 5000 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 reserved 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.
SEE ALSO
intro(4),
ioasic(4),
ttys(5),
MAKEDEV(8)
HISTORY
The
scc driver first appeared in
4.4BSD.
The
scc driver was also used for the IOASIC SCC found in DEC
Alpha model 3000 TurboCHANNEL based systems;
NetBSD/alpha has since been converted to use the
machine-independent
zstty(4).
BUGS
The IOASIC provides internal DMA channels that can be programmed to transfer up
to 4096 bytes of data into, or out, of an SCC without further software
intervention. This feature of the IOASIC 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 mapping, 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.