This application note contains information on the DL3500-Modbus to DH-485 interface. The DL3500 model contains
two modes of operation, Modbus Master and Modbus Slave, which are selectable by the PC Configuration Software.
The latest version is available on the web at
http://www.equustek.com/downloads.html
The information contained in this application note is supplementary information specific to Modbus not contained in
the regular User's Guide.
Master or Slave mode?
This application note is divided into two parts, Modbus Master and Modbus Slave modes; they correspond to the mode
the DL3500 is going to be on the Modbus Network, and which side either DH+ or Modbus the commands will be
initiated on.
Master mode is used when a device on the DH+ network is going to initiate all communications with one or many
Modbus slave devices.
Please Refer to DL3500-DH-485/Modbus Master Application note.
Slave mode is used when a device on the Modbus network is going to initiate all communications with one or many
SLC’s, PLC’s or other DH+ devices.
Please Refer to DL3500-DH-485/Modbus Slave Application note.
The application notes generally assume that a SLC or other DH-485 device which can originate commands to Modbus
via a DL3500 in master mode, or responding to Modbus commands via a DL3500 in slave mode. Only devices capable
of transmitting DH-485 message commands in PLC5 (or PLC3) format and able to receive DH-485 message
commands in PLC5 format can be used with the DL3500-Modbus/DH-485 including SLC’s, MicroLogix’s,
ControlLogix’s and HMIs as well as other intelligent devices.
Due to differences between DH-485 and Modbus protocols and the universal design of the DL3500 there are
differences between the lengths of messages, error handling and addressing which have to be carefully considered by
the Systems Designer, Programmer and Installer.
CAUTION:
Incorrect configuration may result in unsafe operation, damage to equipment or safety hazard to personnel.
Read the DL3500 User's Guide and the appropriate application notes carefully before putting a DL3500 on-line.
The hardware and software must be fully tested off-line in a safe “TEST” environment prior to putting the unit on-line
in an operational environment.
DL3500-DH-485 MODBUS MASTER TO A-B DH-485 CONFIGURATION
Use this option when the is required to be the master on a Modbus network.
The Modbus Master Application notes contain configuration information for the DL3500-DH-485 protocol and should
be used in conjunction with the DL3500 User's Guide.
DL3500-DH-485 MODBUS SLAVE TO A-B DH-485 CONFIGURATION
Use this protocol when the is required to be a slave device on a Modbus network.
The Modbus Master Application notes contain configuration information for the DL3500-DH-485 protocol and should
be used in conjunction with the DL3500 User's Guide.
NOTES:
1. The unit that you have received can be configured as Modbus Master or Modbus Slave.
Ensure that you understand and carefully follow the specific configuration procedures for the Modbus protocol.
2. There are significant differences between the configuration, programming and operational requirements
of Modbus Master and Modbus Slave protocols.
3. If you configure the DL3500 for Modbus Master Operation it must be the only master on the Modbus network.
A station on DH-485 originates commands to the DL3500-DH-485 Modbus Master that then re-transmits them
over Modbus to a Modbus Slave device. Other intelligent DH-485 devices capable of initiating DH-485
messages in PLC5 (or PLC3) format and able to receive PLC5 message commands could also be used as the DH-
485 “master”.
4. Be sure to fully test the hardware and software off-line to ensure that you understand its configuration
and operation. Prior to putting the DL3500 on-line in an production process, the operation of the complete
system should be fully tested on-line in a safe "test" environment.
5. Due to differences between DH-485, Modbus and the hardware and software there are differences
between the lengths of messages, error handling and addressing which have to be carefully considered by the
Systems Designer, Programmer and Installer.
6. Additional literature regarding DH-485, Modbus and PLC products can be obtained from Modicon and A-B.
Suggested reference materials for A-B DH-485 protocol is shown in section 1.7 of the User's Guide.
CAUTION:
Incorrect configuration may result in unsafe operation, damage to equipment or safety hazard to personnel.
Read the DL3500 User's Guide and the appropriate application notes carefully before putting a DL3500 on-line.
The DL3500 hardware and software must be fully tested off-line in a safe “TEST” environment prior to putting the unit
on-line in an operational environment.
Contact Technical Support if you need further information or assistance.
The following table provides a reference between the different radixes used for your reference
DECIMAL TO OCTAL TO HEXADECIMAL ADDRESS CONVERSION TABLE
APPLICATION NOTE
DL3500-DH-485 MODBUS SLAVE PROTOCOL
The information contained in this configuration guide is for the Modbus Slave protocol only, and is supplementary
to the information in the User's Guide.