Basler DECS-200 User Manual

Modbus™ Communication DECS-200
7-4
DETAILED MESSAGE QUERY AND RESPONSE
A detailed description of DECS-200 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.
Response
The response message contains the data queried. The data block contains the block length in bytes
followed by the data for each requested register. For each requested register, there is one Data Hi and
one Data Lo. Attempting to read an unused register or a register that does not support a read results in
an error response with the exception code for an illegal data address. If the query is a broadcast (device
address = 0), no response message is returned.
Maximum response message length obtained for query of 125 registers is 5 + (125 x 2) = 255 bytes.
Device
Address
Function
Code = 03
Byte
Count
Data
High
Data
Low
For each
requested
register
Data
High
Data
Low
CRC
Low
CRC
High
250
max.
First
queried
register
High
First
queried
register
Low
Data High
and data
Low
Last
queried
register
High
Last
queried
register
Low
Preset Multiple Registers
A preset multiple registers query could address multiple registers in one slave or multiple slaves. If the
query is broadcast (device address = 0), no response is required.
Query
A Preset Multiple Registers query message requests a register or block of registers to be written. The
data block contains the starting address and the quantity of registers to be written, followed by the Data
Block byte count and data. The DECS-200 will perform the write when the device address is the same as
the DECS-200 remote address or when the device address is 0. A device address is 0 for a broadcast
query.
A register address of N will write Holding Register N+1.
All Modbus Generic Data Formats can be loaded by this function (see
Data Formats ).
No data will be written if any of the following exceptions occur:
• Queries to write to Read Only or unsupported registers result in an error response with an exception
code of Illegal Data Address.
• Queries attempting to write more than 100 registers cause an error response with an exception code
of Illegal Function.
• An incorrect Byte Count will result in an error response with an exception code of “Illegal Function.”
• A query to write an illegal value (out of range) to a register results in an error response with an
exception code of Illegal Data Value.
• Query Starting Register address is mapped to DECS-200 Modbus address space but is not
referenced to the lower order 16 bits of the assigned application data. (See explanation in
Data
Formats
.)

Basler DECS-200 Specifications

General

Brand	Basler
Model	DECS-200
Category	Controller
Language	English