User's Manual

Hi-G-Tek Ltd. Microelectronics & Asset Tracking Technology
106
5
System
5.7.2.3. Reader Session Retransmissions.
Probability calculations were used to estimate Reader Session
retransmissions when creating System Sessions. However, it is
advisable that suitable retransmissions be on hand at the
application level to overcome unpredictable radio interference.
The actual number of retransmissions can be either fixed or
dynamic. These should be set in accordance with the application
requirements and the empirically evaluated on-site electromagnetic
characteristics.
5.7.2.4. Line Communication RS-485 Layout
The connection of many Readers to a Local Site Controller (LSC)
is done via the RS-485 protocol. Up to 32 Readers may be
connected to one COMM Port, depending on the type of RS-485
to RS-232 converter used.
Two topologies can be used:
A long daisy chain connection, where all the readers are
connected in one long line.
A star-type connection, where the readers are split into groups
and each group is connected directly to the converter.
It is recommended that the second alternative be used wherever
possible. A star-type connection provides redundancy in terms of
connections. This alternative is also preferable from the power
supply point of view, as only one power supply for the Readers is
necessary. The power supply should be located near the converter.
When the line is divided into segments, the voltage drop along the
segments is smaller.