BACtalk® Field-Level Gateway

for Modbus
Features and highlights
• Interoperable
BACnet-compliant on MS/TP LAN
at up to 76.8 Kbps.

• Versatile
Supports 100 analog and 100
binary values to integrate Modbus
device data with a BACnet system.

• Reliable
AZ60 processor, with all program
data backed up in nonvolatile flash
memory.

• Economical
Simple, low cost solution for
field-level integration of Modbus
devices.

• Flexible
Offers user-configurable poll
delay, response timeout and
unreliable threshold for increased
compatibility with other Modbus
devices.

The Alerton ® FLG-MODBUS is a field-level gateway that resides on

a BACnet MS/TP network and connects to Modbus over EIA-232 or
EIA-485, translating Modbus data to BACnet AVs and BVs. EIA-232 can
interface to a single Modbus device; EIA-485 can interface to up to 10
Modbus devices (with a valid address between 1–247). The FLG-MODBUS
appears to the BACnet system as a single BACnet device instance.

The FLG-MODBUS offers a point capacity of 100 BACnet AVs and 100
BVs—an ideal point count for most Modbus applications such as chillers
and VFDs. A single FLG-MODBUS supports up to 10 Modbus devices on
a multi-drop Modbus EIA-485 network. A DB-9 connector supports a point-
to-point connection to a Modbus device over Modbus EIA-232.

High baud rates of 4800, 9600, 19200, 38400, 76800 and 115200
baud provide fast transactions. User-configurable poll delay, response
timeout and unreliable threshold enable users to futher customize the
FLG-MODBUS operation. Enhanced diagnostics facilitate
troubleshooting.

The FLG-MODBUS features an AZ60 processor. All configuration data

is backed up in nonvolatile flash memory. An MS/TP header provides for
connection of an Alerton FST-100 with an AC-2680 cable, which is helpful
for troubleshooting and field service.

6670 185th Avenue Northeast, Redmond, WA 98052 USA • Tel: 425.869.8400 • Fax: 425.869.8445 • www.alerton.com

2 of 2 LTBT-FLGMDBS Rev. 0003
© Honeywell International Inc. All rights reserved. Alerton is a registered trademark of Honeywell.
 BACtalk® Field-Level Gateway
Technical data
for Modbus
• Power 24 VAC @ 5 VA. Utilizes a half-wave rectifier, which allows a single
transformer to power multiple devices. One leg of 24 VAC connects to earth 3 9/32" (83mm)

(panel) ground. 1 15/32" (37mm)

• Processor and Memory Motorola AZ60 processor with on-board flash 7/32" (5mm)

memory. Flash memory provides nonvolatile program and data storage, 24VAC

GND

and allows for encrypted updates to the program for future product FLG-MODBUS
ASSEMBLED IN USA
POWER STATUS

enhancements. POWER: 24 VAC @ 24VAC - 1

0.5A MAX GND - 2
CLASS 2 CIRCUITS
ONLY
USE COPPER
CONDUCTORS ONLY STATUS

•
FOR INDOOR USE ONLY

LBL-FLG-MB-A
SUITABLE FOR PLENUM MOUNTING

Max. Dimensions 4.75” (120mm)H x 3.25” (83mm)W x 1.13” TUX/MODBUS

STATUS
MODBUS STATUS

SW2 = MS/TP MAC ADDR

EIA-232 / 485
(DB-9)

(28mm)D.
VALUE EIA-232
MODBUS
SW2 ON CONFIG.
1 1
2 2 JUMPER
3 4 1 2 3
8
4 23/32" (120mm)
4
5
6
16
32
4 5/16" (109mm)

•
7 64 EIA-232
EIA-485 DB

Terminations Removable header-type screw terminals for BACnet MS/TP MS/TP

MS/TP STATUS

SW3 MODBUS SETTINGS

SWITCH NUMBER

and Modbus EIA-485 accept 14–24 AWG wire. Male DB-9 connector for
OFF ON
STATUS 1 RTU ASCII
2 NO PARITY PARITY
SW3 3 ODD PARITY EVEN PARITY
4 9600 BAUD 4800 BAUD

Modbus EIA-232.
5 STANDARD 1 STOP BIT
6 (NOT USED)
+
7 (NOT USED) MODBUS
-
(B) + - 3
EIA-485
(W) - - 4

•
OPEN ENERGY

+
MANAGEMENT

Environmental 0–158 deg. F (-17–70 deg. C). 0–95% RH, non-

EQUIPMENT 5K05

OPTION (B) + - 5
MS/TP MS/TP
(W) - - 6
+ -
MS/TP

condensing.
-

• Modbus Communications Either EIA-232 (serial cable) to single

1/2" (12mm)
Modbus device or multi-drop EIA-485 (twisted pair) to up to 10 Modbus
devices. Network options configurable for ASCII/RTU, 4800, 9600, 19200,
38400, 76800 and 115200 baud, even/odd/no parity, and stop bit options for
compatibility with various Modbus implementations.

• BACnet Communications BACnet MS/TP LAN with auto-detection of

MS/TP communications rate up to 76.8 Kbps.

• Software Support for 100 BACnet AVs and 100 BACnet BVs, each
mapped to a Modbus data point through a string written to the description
property of the AV or BV object.

• Ratings

Listed Underwriters Laboratory for Open Energy Management Equipment

(PAZX) under the UL Standard for Safety 916; listing includes U.S. and
Canadian certification

Suitable for plenum mounting

EMC Directive 89/336/EEC (European CE Mark)

FCC Part 15, Subpart J, Class A

Ordering information
Item number Description

FLG-MODBUS BACtalk field level gateway for

Modbus

Specifications subject to change without notice

6670 185th Avenue Northeast, Redmond, WA 98052 USA • Tel: 425.869.8400 • Fax: 425.869.8445 • www.alerton.com

2 of 2 LTBT-FLGMDBS Rev. 0003
© Honeywell International Inc. All rights reserved. Alerton is a registered trademark of Honeywell.