6
2.4 Serial Communication Interfaces (For Models with RS485 Port)
The iSeries controller/monitor with the Embedded Ethernet Server option board support
only RS485/422 interfaces. These standards define the electrical characteristics of a
communication network. The RS485 port of the Ethernet Server is fully compatible for
use with RS422 instruments. The RS485 is an extended version of the RS422
communication standard which increases the allowable number of devices from 10 to
32 by improving the electrical characteristics.
• The
RS485
standard (
multi-point
) allows one or more devices (multi-dropped) to be
connected to the Ethernet Server using a two-wire connection (half-duplex) +Rx/+Tx
and –Rx/-Tx. Use of RS485 communications allows up to 32 devices to connect to the
Web Server with cable length up to 4000 feet long.
Although the RS485 is commonly referred to as a "two wire" connection, the
Web Server also provides a ground/return shield connection to use as a
common connection for EMI noise protection.
Table 2.2
shows some characteristics of the RS485 communication interface.
Table 2.2 Data Transmission Characteristics RS485
Data Transmission Characteristics
RS485
Transmission Mode
Differential
Electrical connections
2 wire
Drivers per line
32 drivers
Receivers per line
32 receiver
Maximum data rate
10M bits/s
Maximum cable length
4000 ft (1200 meters)
