HONEYWELL IDENTIPOINT™ INTELLIGENT SMARTCARD SYSTEM
39
95-7767
Table 9. IOM Switch Functions
Table 10. IOM S1 DIP switch settings
Table 11. IOM S3 DIP switch settings
RS485 Communication and
Termination Setting
CAUTION
If the Bus wiring enters or exits the building, the
protectors listed in Table.13 must be used. Bus
length for RS485 must not exceed 500 m end-to-
end.
RS485 is a 2-wire balanced multi-drop serial bus, which
allows a master unit to send and receive data to and from its
slave units. When an IdentIPoint reader is connected to one or
more IOMs, the reader is the master unit while the IOMs are
the slave units. Each unit, having its own RS485 address, is
connected in parallel to the RS485 bus. The length of the bus
must not exceed 1640 ft (500 m), end-to-end. The master
always assumes address zero. The master facilitates the
communication of data between itself and a particular slave
unit in a particular instance. For IOM address setup, see
section
IOM Address Set up
of
Connector and Switch
Descriptions
topic.
The RS485 serial signal travels down the stream, usually over
unshielded twisted pair cables. A suitable termination resistor
has to be put at the end of the RS485 line to absorb the
remaining energy on the line to prevent signal reflection. A
100 ohm resistor is chosen as it stays closest to the
characteristic impedance of the transmission line.
IdentIPoint readers and IOMs are both equipped with a
termination circuit and do not need an external termination
resistor. Setting bit 2 on S1 DIP switch to ON introduces a
termination resistor on the RS485 line. The units that sit
physically on both ends of an RS485 bus should have their
RS485 termination turned on. To minimize error signals
induced on the RS485 bus during its high-impedance state, it
is also recommended to turn on the pull-up and pull-down
resistors in the IdentIPoint reader (master) as shown in Fig.
30. See Table.7 and Table.10 for S1 DIP switch settings for
readers and IOM.
Switch
Description
S1
RS485 Termination Control DIP
switch
S2
Initialization Button
S3
IOM Address set up DIP switch
S4
Cover tamper detection switch
Position
Description
1
RS485-A pull up
2
RS485 Termination
3
RS485-B pull down
4
Reserved
Position
Description
1
Address value 1
2
Address value 2
3
Address value 4
4
Address value 8
5
Address value 16
6
Address value 32
7
Address value 64
8
For IOM setup, normally set to OFF
