LINEPULS & LINECOD catalogue 2016 in English

LINECOD
Absolute output circuits and fieldbus interfaces
The absolute position information can be provided to the following control via a wide variety
of output circuits (interfaces).
Typically, we can distinguish between electrical interfaces (serial and analogue interfaces)
and fieldbus interfaces.
The absolute linear encoders are customarily fitted with serial (SSI, BiSS, RS-485) output
circuits, the analogue circuit is more seldom used. The electrical interfaces are simple, costeffective
and easily fulfil the requirements of most industrial applications. Nevertheless in
the last years fieldbus interfaces are rapidly gaining ground worldwide because of their
compatibility in more complex installations.
Fieldbus technology in fact permits to improve performances thanks to complete device
interface (bi-directional data transmission, enhanced programmability, diagnostic information,
etc.), achieve communication transparency, simplify and standardize installations
allowing several devices to be simply connected in the same network.
In addition the use of standardised bus cables provides a simplified and safe connectivity
thus saving time and money whilst reducing the risk of errors.
To meet the industry's request for fieldbus and Ethernet networks and communication
protocols, Lika Electronic has designed the range of IF55 gateways. They are specifically
engineered to interface SSI serial encoders and integrate them easily into conventional
fieldbus and industrial Ethernet networks.
For complete information please refer to the section “IF55 converter series” on page 47.
SSI (the acronym for Synchronous Serial Interface) is a synchronous point-to-point serial
interface engineered for unidirectional data transmission between one Master
and one Slave. Developed in the first eighties of the last century, it is based on the RS-422
serial standard. Its most peculiar feature is that data transmission is achieved by synchronizing
both the Master and the Slave devices to a common clock signal generated by the
controller; in this way the output information is clocked out at each controller request.
Furthermore only two pairs of twisted wires are used for data and clock signals, thus a sixwire
cable is required.
The main advantages in comparison with competing parallel or asynchronous data transmissions
are:
• less conductors are required for transmission;
• less electronic components;
• possibility of insulating the circuits galvanically by means of optocouplers;
• high data transmission frequency;
• hardware interface independent of the resolution of the absolute encoder.
Furthermore the differential transmission increases the noise immunity and decreases the
noise emissions. It allows multiplexing from several encoders, thus process controls are more
reliable with simplified line design and easier data management.
In addition, SSI encoders can be easily integrated into conventional fieldbus or industrial
Ethernet networks using IF55 converters (see on page 47).
Data transmission is carried out as follows.
At the first falling edge of the clock signal (1, the logic level changes from high to low) the
absolute position value is stored while at the following rising edge (2) the transmission of
data information begins starting from the MSB.
36