NAME
scc —
Zilog 8530 Serial Communications
Controller interface
SYNOPSIS
scc* at ioasic? offset ?
DESCRIPTION
Thescc 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
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.