The Modbus Interface Module
Installation & Commissioning Handbook, User Guide, AutroSafe Interactive Fire Alarm System, P-BSL330/IE,
Autronica Fire and Security AS
Page 7
2. The Modbus Interface Module
2.1 Description
The BSL-330 module is an RS-232/422/485 interface module used to
interface various PLC equipment (Programmable Logic Controllers) to
the AutroSafe Interactive Fire Alarm System. The module is both a
physical and a logic protocol converter. At the physical connection
level, it transforms an RS232 connection to an RS485 or RS422
connection. This is convenient as this type of connection is safer in
noisy environments.
The module is connected to the AutroSafe via the AutroCom protocol.
It communicates with both protocols by means of the conversion
software.
A master Modbus device polls the BSL-330 module for reading its
registers. It expects a response within a defined time period.
Communication can be over various serial mediums. The one used
here is the MODBUS RTU protocol over an RS485 link. The
communication is set at 9600 baud, 8 data bits, 1 stop bits and no
parity.
The BSL-330 module allows:
•
detector statuses on the AutroSafe to be made available to a
Modbus PLC
•
users to send basic commands to the AutroSafe from a Modbus
PLC
The Modbus PLC acts as “master” to the BSL-330, and the AutroSafe
as “slave” to the BSL-330. The AutroSafe appears to the Modbus PLC
as a Modbus slave.
For information on
Communication,
refer to section 5.3.1.
The BSL-330 module has the following features:
•
DIN-rail enclosure with removable screw terminals; fits 35mm
symmetric rails
•
DC power input in the range +7V to +35V; uses a high efficiency
switching power supply
•
Two serial ports: Port 1 and Port 2; isolated from each other and
from the power supply
•
Port 1 is RS-232; Port 2 is RS-422/485
•
Controlled slew rate drivers on RS-422/485 ports - no terminators
needed for cables shorter than 300m
•
Internal pull-up/pull-down resistors on RS-422/485 ports ensure
that RS485 bus floats to a valid state when not driven
