Basler Electric DECS-400 - Manual (Page 218)

206 9369700990 Rev R
Code Name Meaning
02 Illegal Data
Address
A register referenced in the data block does not support queried read/write;
For Function Codes 3 and 16 additionally:
1. Starting Register address is mapped to DECS-300 Modbus™ address
space, but is not referenced to the highest order 16 bits of the assigned
application data (see explanation in 2.7 Data Formats), and
2. The number of registers is too small to hold entire value of all data
(variables) assigned to those registers (see explanation in 2.7 Data
Formats).
03 Illegal Data
Value
A preset register data block contains an incorrect number of bytes or one or
more data values out of range.
Communication Hardware Requirements
RTU Communication Requirements
The DECS-400 RS-485 physical interface consists of a three-position terminal strip with terminals for
Send/Receive A (A), Send/Receive B (B), and Signal Ground (C).
TCP Communication Requirements
The DECS-400 Ethernet port uses a RJ-45 connector. The DECS-400 supports 10BASE-T using Cat 5 or
Cat 5e shielded twisted conductor pairs.
Modbus
™/TCP
The Ethernet-enabled interface uses the Transmission Control Protocol/Internet Protocol (TCP/IP) to
encapsulate Modbus messages. The DECS-400 comes with DHCP (Dynamic Host Configuration
Protocol) enabled. A maximum of four simultaneous Modbus TCP/IP connections are possible with the
DECS-400. Information about setting a static IP address (recommended) or using BESTCOMS Device
Discovery feature is provided in the BESTCOMS Software chapter.
Ethernet configuration settings cannot be changed with Modbus register writes. BESTCOMS must be
used to configure DECS-400 Ethernet settings. The front-panel display (Modbus, Ethernet and NTP)
screens can be used to view the Modbus and Ethernet settings. See the Human-Machine Interface
chapter for details.
Detailed Message Query and Response
A detailed description of DECS-400 supported message queries and responses are provided in the
following paragraphs.
Read Holding Registers
Query
This query message requests a register or block of registers to be read. The data block contains the
starting register address and the quantity of registers to be read. A register address of N will read holding
register N+1.
Device
Address
Function
Code =
03
Starting
Address
High
Starting
Address
Low
No. of
Registers
High
No. of
Registers
Low
CRC
Low
CRC
High
The number of registers cannot exceed 125 without causing an error response with the exception code
for an illegal function.
Modbus™ Communication DECS-400