ABB FMBT-21, User Manual

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Historically, Modbus client devices used 5-digit decimal addresses from 40001 to
49999 to represent Holding register addresses. 5-digit decimal addressing limited to
9999 the number of holding registers that could be addressed.
Modern Modbus client devices typically provide a means to access the full range of
65536 Modbus Holding registers. One of these methods is to use 6-digit decimal
addresses from 400001 to 465536. This manual uses 6-digit decimal addressing to
represent Modbus Holding register addresses.
Modbus client devices that are limited to 5-digit decimal addressing may still access
registers 400001 to 409999 by using 5-digit decimal addresses 40001 to 49999.
Registers 410000-465536 are inaccessible to these clients.
Function codes
The adapter module supports the Modbus function codes shown below.
Description Name Function code
Reads the contents of a contiguous block of holding
registers in a server device. Read Holding Registers 03h
Writes a single holding register in a server device. Write Single Register 06h
Writes the contents of a contiguous block of hold-
ing registers in a server device. Write Multiple Registers 10h
Writes the contents of a contiguous block of hold-
ing registers in a server device, then reads the
contents of a contiguous block of holding registers
(same or different than those written) in a server
device. Read/Write Multiple Registers 17h
Allows reading identification and other information
of the server. Encapsulated Interface Trans-
port / Read Device Identifica-
tion 2Bh/0Eh
Parameter "Read Device ID code" allows one to
define three access types:
• 01: Request to get the basic device identification
(stream access)
• 02: Request to get the regular device identifica-
tion (stream access)
• 04: Request to get one specific identification
object (individual access).
Encapsulated Interface Transport / Read Device
Identification
The adapter module supports the Modbus EIT/RDI objects shown below.
Name Object ID
Vendor Name 00h
Product Code 01h
Major/Minor Revision 02h
Vendor URL 03h
Product Name 04h
48 Modbus/TCP – Communication protocol