The Zilog 8530 provides two serial input/output channels capable of supporting a variety of communication protocols. A typical system uses two or more of these devices to implement essential functions, including RS-423 ports (which also support most RS-232 equipment), and the console keyboard and mouse devices.

The zs module is a loadable STREAMS driver that provides basic support for the Zilog 8530 hardware and basic asynchronous communication support. The driver supports the termio(7I) device control functions specified by flags in the c_cflag word of the termios structure and by the IGNBRK, IGNPAR, PARMRK, or INPCK flags in the c_iflag word. All other termio(7I) functions must be performed by STREAMS modules pushed atop the driver. When a device is opened, the ldterm(7M) and ttcompat(7M) STREAMS modules are automatically pushed on top of the stream, providing the standard termio( 7I) interface.

The character-special devices /dev/term/a and /dev/term/b are used to access the two serial ports on the CPU board.

Valid name space entries are /dev/cua/[a-z], /dev/term/[a-z] and /dev/tty[a-z]. The number of entries used in a name space are machine dependent.

The /dev/tty[n] device names only exist if the SunOS 4.x Binary Compatibility Package is installed. The /dev/tty[n] device names are created by the ucblinks command, which is available only with the SunOS 4.x Binary Compatibility Package.

To allow a single tty line to be connected to a modem and used for both incoming and outgoing calls, a special feature is available that is controlled by the minor device number. By accessing character-special devices with names of the form /dev/cua/[n], it is possible to open a port without the Carrier Detect signal being asserted, either through hardware or an equivalent software mechanism. These devices are commonly known as dial-out lines.

Once a /dev/cua/[n] line is opened, the corresponding tty line cannot be opened until the /dev/cua/n line is closed. A blocking open will wait until the /dev/cua/[n] line is closed (which will drop Data Terminal Ready, and Carrier Detect) and carrier is detected again. A non-blocking open will return an error. If the tty line has been opened successfully (usually only when carrier is recognized on the modem) , the corresponding /dev/cua/[n] line cannot be opened. This allows a modem to be attached to /dev/term/[n] (renamed from /dev/tty[n]) and used for dial-in (by enabling the line for login in /etc/inittab) and also used for dial-out (by tip(1) or uucp(1C)) as /dev/cua/[n] when no one is logged in on the line.

The zs module supports the standard set of termio ioctl() calls.

If the CRTSCTS flag in the c_cflag field is set, output will be generated only if CTS is high; if CTS is low, output will be frozen. If the CRTSCTS flag is clear, the state of CTS has no effect.

If the CRTSXOFF flag in the c_cflag field is set, input will be received only if RTS is high; if RTS is low, input will be frozen. If the CRTSXOFF flag is clear, the state of RTS has no effect.

The termios CRTSCTS (respectively CRTSXOFF) flag and termiox CTSXON (respectively RTSXOFF) can be used interchangeably.

Breaks can be generated by the TCSBRK, TIOCSBRK, and TIOCCBRK ioctl() calls.

The state of the DCD, CTS, RTS, and DTR interface signals may be queried through the use of the TIOCM_CAR, TIOCM_CTS, TIOCM_RTS, and TIOCM_DTR arguments to the TIOCMGET ioctl command, respectively. Due to hardware limitations, only the RTS and DTR signals may be set through their respective arguments to the TIOCMSET, TIOCMBIS, and TIOCMBIC ioctl commands.

The input and output line speeds may be set to any of the speeds supported by termio. The input and output line speeds cannot be set independently; for example, when you set the the output speed, the input speed is automatically set to the same speed.

When the driver is used to service the serial console port, it supports a BREAK condition that allows the system to enter the debugger or the monitor. The BREAK condition is generated by hardware and it is usually enabled by default. A BREAK condition originating from erroneous electrical signals cannot be distinguished from one deliberately sent by remote DCE. The Alternate Break sequence can be used to remedy this.

Due to a risk of incorrect sequence interpretation, binary protocols such as PPP, SLIP, and others should not be run over the serial console port when Alternate Break sequence is in effect. By default, the Alternate Break sequence is three characters: carriage return, tilde and control-B (CR ~ CTRL-B), but may be changed by the driver. For more information on breaking (entering the debugger or monitor, see kbd(1) and kb(7M).

An open will fail under the following conditions:

ENXIO

The unit being opened does not exist.

EBUSY

The dial-out device is being opened and the dial-in device is already open, or the dial-in device is being opened with a no-delay open and the dial-out device is already open.

EBUSY

The port is in use by another serial protocol.

EBUSY

The unit has been marked as exclusive-use by another process with a TIOCEXCL ioctl() call.

EINTR

The open was interrupted by the delivery of a signal.

/dev/cua/[a-z]

dial-out tty lines

/dev/term/[a-z]

dial-in tty lines

/dev/tty[a-z]

binary compatibility package device names

See attributes(5) for descriptions of the following attributes:

eeprom(1M), kadb(1M), tip(1), ucblinks(1B), cu(1C), uucp(1C), ports(1M), ioctl(2), open(2), attributes(5), zsh(7D), termio(7I)ldterm(7M), ttcompat(7M), kb(7M), ldterm(7M)

zsn: silo overflow.

The Zilog 8530 character input silo overflowed before it could be serviced.

zsn: ring buffer overflow.

The driver's character input ring buffer overflowed before it could be serviced.