2014-
02
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Commands
read/write multiple registers (17h)
This MODBUS command combines the functionality of the
read holding registers
command
with the
write multiple registers
command. This command should always be used when data
is exchanged cyclically via a controller. The following should be noted:
If an identification command is initiated via this MODBUS command (for example, a read
command), the answer to this command is not included in the response associated with this
request. The data is only available after the time required to process the command has
elapsed.
If an identification command is initiated several times (e.g., if you wish to execute a read
command several times in succession), the first four bytes of the identification telegram must
be modified accordingly. The toggle bit can be used for this.
Process:
1. A request is issued. The following parameters must be known here:
Writing:
2002d
High byte
Byte 2
Command code
19h
enhanced read
command
Low byte
Byte 3
Word number/Channel/
Toggle bit
04h
Word count = 0.
4 corresponds to
channel 2. Channel
number shifted 1 bit to
the left.
2003d
High byte
Byte 4
Status
05h
05h = identification
read error (meaning of
the identification
statuses see chapter
Low byte
Byte 5
Reply counter
02h
Increases by 1 after
each additional
response.
2004d -
2011d
High byte
Data
00h
No data read because
no data carrier in front
of the read head.
Low byte
Data
00h
No data read because
no data carrier in front
of the read head.
Table 7.12
Response to the executed identification command
enhanced read
Address
(0-based)
Register division
Byte number of the
identification
telegram
Use
Contents Meaning
Note!
If a type IPC03 data carrier is held in front of the reading head, the data can be viewed if a
read
holding registers
command is executed repeatedly.
Start address (depending on channel)
Channel 0
0d
Channel 1
1000d
Channel 2
2000d
Channel 3
3000d
Channel 4
4000d
Number of registers to be written:
Maximum 121d
Table 7.13
Parameters required for a request
