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Glossary
890USE19600 April 2004 61
MAC address media access control address. A 48-bit number, unique on a network, that is
programmed into each network card or device when it is manufactured.
mandatory
module
When an Advantys STB I/O module is configured to be mandatory, it must be
present and healthy in the island configuration for the island to be operational. If a
mandatory module fails or is removed from its location on the island bus, the island
will go into a pre-operational state. By default, all I/O modules are not mandatory.
You must use the Advantys configuration software to set this parameter.
master/slave
model
The direction of control in a network that implements the master/slave model is
always from the master to the slave devices.
Modbus Modbus is an application layer messaging protocol. Modbus provides client and
server communications between devices connected on different types of buses or
networks. Modbus offers many services specified by function codes.
MOV metal oxide varistor. A two-electrode semiconductor device with a voltage-
dependant nonlinear resistance that drops markedly as the applied voltage is
increased. It is used to suppress transient voltage surges.
MSB most significant bit, most significant byte. The part of a number, address, or field that
is written as the leftmost single value in conventional hexadecimal or binary notation.
N.C. contact normally closed contact. A relay contact pair that is closed when the relay coil is de-
energized and open when the coil is energized.
N.O. contact normally open. contact. A relay contact pair that is open when the relay coil is de-
energized and closed when the coil is energized.
NEMA National Electrical Manufacturers Association.
network cycle
time
The time that a master requires to complete a single scan of all of the configured I/
O modules on a network device; typically expressed in microseconds.
M
N