Envoy Application Programming Manual

Glossary
Envoy Application Programming Manual—427159-001
Glossary-6
logical device number
low-cost nodes can be connected. One or more LANs can be connected to the system
such that the LAN users can access the system as if their workstations were connected
directly to it.
logical device number. A number that identifies a particular I/O device in the system.
Logical device numbers are assigned to physical I/O devices.
low PIN. A PIN that ranges from 0 through 254. See also high PIN.
MCW. Message control word. The first 2 bytes (one word) of the application buffer, used by
Envoy to build the control and address fields of the frame.
message. The information transmitted over a communications line as a result of a single call
to a READ, WRITE, or WRITEREAD procedure.
modifier. A word used when a device is added to override preset characteristics or to describe
additional characteristics of a device or a process.
multidrop. Same as multipoint.
multipoint. A data-link configuration in which one station is designated as the supervisor and
controls all communications over the link. The other stations are designated as
tributaries.
NAK. See negative acknowledgment (NAK).
negative acknowledgment (NAK). In byte-synchronous transmission, a line-control
character sent by a receiving terminal to indicate that an error was encountered in the
previous transmission and that the receiving terminal is ready to accept another
transmission. NAK is also the “not ready” reply to a station selection (multipoint) or to
an initialized sequence (line bid) in point-to-point operation. See also affirmative
acknowledgment (ACK).
noncontinuous polling. This type of polling defines a specific number of cycles that the
tributary stations included in the address list are to be polled.
nonsensitive command. A DSM command that can be issued by any user or program
allowed access to the target subsystem. See also sensitive command.
nonswitched. A line configuration that provides a permanent path between two stations. This
path can be either a privately owned cable or a dedicated path leased from a common
carrier.
object. One or more of the devices, lines, processes, and files in a Compaq subsystem; any
entity subject to independent reference or control by one or more subsystems. In the
Subsystem Control Facility (SCF), an object is a resource controlled by a subsystem.
Objects include processes, disk files, data communications lines, display devices, and
groups of devices or communications lines. Each object has an object type and an object
name. The object type describes the type of the object, such as LINE, SU (subdevice),