Communications
50
All information transferred between the master and slave
devices is sent within a SEAbus protocol message packet.
SEAbus is a byte-count oriented open protocol originally devel-
oped for ACCESS communications between the devices. Each
ACCESS device supports the SEAbus protocol.
The SB Energy-Comm trip unit is one of several field devices that
can communicate with a monitoring supervisory device in an
ACCESS supervisory and control system. In order to communi-
cate in an ACCESS system, the device must be connected using
the EIA-485 network connection. This connection is through the
rear connector of the SB Energy-Comm trip unit. EIA-485 commu-
nication can be used to concurrently connect up to thirty-two
remote devices on a single communications loop. Each device is
given an address, a unique unit ID (identification number). In this
way, each remote device may be monitored and controlled from
one location by a single computer or PLC. For more information
on setting up and installing an ACCESS system network, see
I
nstalling the ACCESS System
.
Figure 10.1
Typical ACCESS Communications System
10.5 Setting the Address and Baud Rate
Before communication with the host computer/PLC is possible,
users must ensure that the SB Energy-Comm trip unit and all
other connected devices are configured for the required com-
munications standard (EIA-232 or EIA-485).
The next step is to program the communication parameters of
the SB Energy-Comm trip unit and all other connected devices.
The Address and Baud Rate parameters of the SB Energy-
Comm trip unit can be programmed via the front panel. The
address is the number that will uniquely represent the trip unit
as a unique slave device in a master/slave system. It must be
set to a unique value between 1 and 254.
To configure the device address, select
Slave Address
form
the
Communications Menu
. The following screen appears:
Use the Up and Down Arrow keys to select the value for
each digit. Press Enter to move between digits. Press
Escape to set the new address and then exit.
The baud rate of each device on the network must be set to
correspond with the baud rate selected from the computer.
Options include 1200, 2400, 4800, 9600 or 19,200 baud.
To change the baud rate, select
EIA 485 Baud Rate
from the
Communications menu.
Use the Up and Down Arrow keys to select the baud
rate. Press Escape then Enter to exit and set the new
baud rate setting.
When using a modem interface between the host computer
and any remote device(s), ensure that the host computer is not
used to set the BAUD RATE parameter of any selected device
outside the working range of the modem. Doing so will cause
that device to cease communicating.
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