Asynchronous Serial Communications Programmer's Reference Manual (32022-90052)

46 Chapter2
Controlling Asynchronous Devices Programmatically
Device Operation Modes
System Console
The CIO system console is the only terminal (or PC) that is not
connected to the system through a DTC. The system is aware of its
existence from system initialization. It is connected to a special
interface card in the system cabinet known as the access port.
The system console has a unique set of functionality not available to
any other device. It can receive console messages, and execute special
commands through use of console attention characters that are not
recognized by any other device.
A subset of console functionality may temporarily be assigned to
another interactive device through use of the :CONSOLE command. This
is called moving the logical console to the device. Any commands
requiring use of the special console attention characters must continue
to be executed from the system console. Note that the logical console
may not be moved to a terminal connected via PAD or to a terminal
with switching enabled.
The system console is also a session-accepting device, and therefore can
be operated as a programmatic device as well. However, because the
console serves a special purpose, some of the features of other
session-accepting devices are not provided:
• The console may not operate at 19200 bps. Supported speeds are
300, 1200, 2400, 4800 and 9600 bps.
• No user block mode applications are supported. Except for NMMGR
which is used to modify configuration files, no VPLUS block mode
applications are supported.
CAUTION The console will continue to display messages it receives even if being
operated in block mode. This may cause data on the block mode screen
to be overwritten or lost.
Spooled Devices
MPE/iX is equipped with a spooling facility to assist the operation of
certain nonsharable devices. When a spooler process controls a
nonsharable device the device gives the appearance of being shared
among several users.
The spooler intercepts data being output by various processes and
temporarily stores it on disk instead of sending it directly to the device.
The disk essentially becomes a staging area, while the spooler manages
the selection of output spool files destined for the spooled device.
Printers are the only type of asynchronous device that can be spooled.
Because it makes no sense for printers to be session-accepting devices
(they can be used for output only), spooled devices are always
programmatic devices.