System Components - Omron CQM1-ARM21 Operation Manual

Introduction

1-1-2 System Components

Master
Slave
Power Supply
Data decoupling
Cable
AS-Interface is a single master - multi slave system. The system requires one
master unit to control all data exchanges over the bus. During normal
operation, the master cyclically sends output data to all slaves, and receives
the slaves' input data in return.
Apart from the cyclic data exchange, the master will search the bus for newly
added slave units, and may send out a specific command to one slave per
bus cycle.
The maximum number of slaves that an AS-Interface master can exchange
I/O data with at any time is 31.
AS-Interface slaves will only respond to master requests containing the
address that they have been set to. Practically all AS-Interface slaves have
their address stored in non-volatile memory. The factory setting is always to
address 0. The address can be changed either by a hand-held addressing
tool, or by a specific master request.
Each slave may have up to 4 bits input plus 4 bits output data, and up to 4
parameter bits. Each I/O combination allowed by the AS-Interface
specification has a unique identification code, which is stored in the slave, and
can be read by the master.
In a fully extended AS-Interface network, the maximum amount of digital I/O
points can be 31 * (4 inputs + 4 outputs) = 248.
The slave's circuitry is generally powered via the AS-Interface line, but in- and
output ports may have a provision for external power supply.
Superimposing communication data on the lines that supply energy to the
slaves creates special requirements for an AS-Interface power supply unit. A
station will communicate by varying its impedance on the AS-Interface line,
thereby generating specifically shaped pulses in the current drawn from the
line.
The data decoupling circuit incorporated in the AS-Interface power supply will
transform these current pulses into voltage variations, which can be detected
by the other stations on the line. In order to allow the whole system to work
reliably, the voltage, current range and impedance of an AS-Interface power
supply must be within the limits specified by the AS-Interface standard.
An AS-Interface power supply should have a minimum rated output current of
2.4 A at a supply voltage of 29.5...31.6V DC.
Although AS-Interface recommends the use of the trademark 'yellow cable'
especially designed for IP67 protection and on-line addition and removal of
slaves, any shielded or unshielded two-wire cable may be used that meets
the following specifications (at a frequency of 167 kHz).
R´/4 L´/4
C´
The recommended cross section is 2 x 1.5 mm²; The maximum allowed
current through the AS-Interface cable is 8A.
Z : 70...140Ω
R´: < 90 mΩ/m
L´: 400...1300 nH/m
G´
C´: < 80 pF/m
G´: < 5 µS/m
Section 1-1
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