Basler Electric DGC-2020HD Modbus Protocol - Manual (Page 12)

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General Information DGC-2020HD Modbus ™ Protocol
CRC Hi error check
CRC Lo error check
Restart Communications Option
This query causes the remote communications function of the DGC-2020HD to restart, terminating an
active listen only mode of operation. No effect is made upon primary relay operations. Only the remote
communications function is affected. If the query is a broadcast (device address = 0), no response
message is returned.
If the DGC-2020HD receives this query while in the listen only mode, no response message is generated.
Otherwise, a response message identical to the query message is transmitted prior to the
communications restart.
Device Address
Function Code =
08 (hex)
Subfunction Hi = 00 (hex)
Subfunction Lo = 01 (hex)
Data Hi = xx (don't care)
Data Lo = xx (don't care)
CRC Hi error check
CRC Lo error check
Listen Only Mode
This query forces the addressed DGC-2020HD to the listen only mode for Modbus communications,
isolating it from other devices on the network. No responses are returned.
While in the listen only mode, the DGC-2020HD continues to monitor all queries. The DGC-2020HD does
not respond to any other query until the listen only mode is removed. All write requests with a query to
Preset Multiple Registers (Function Code = 16) are also ignored. When the DGC-2020HD receives the
restart communications query, the listen only mode is removed.
Device Address
Function Code =
08 (hex)
Subfunction Hi = 00 (hex)
Subfunction Lo = 04 (hex)
Data Hi = xx (don't care)
Data Lo = xx (don't care)
CRC Hi error check
CRC Lo error check
Preset Multiple Registers
A preset multiple registers query could address multiple registers in one slave or multiple slaves. If the
query is a broadcast (device address = 0), no response message is returned.
Query
A Preset Multiple Register 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 DGC-2020HD
will perform the write when the device address in query is a
broadcast address or the same as the DGC-2020HD Modbus Unit ID (device address).
A register address of N will write Holding Register N+1.
Data will cease to be written if any of the following exceptions occur.
• Queries to write to Read Only registers result in an error response with Exception Code of “Illegal
Data Address”.
• Queries attempting to write more than 100 registers cause an error response with Exception
Code “Illegal Function”.