2014-
02
36
Commands
read holding registers (03h)
This MODBUS command (request) can be used to export the input register from the
identification system. When data becomes available, the device writes it to the input register. If
the data is not retrieved immediately, up to 32 responses can be stored temporarily before data
is lost. If no response data is available, the content of the register is 0.
Process:
1. A request is issued. The following parameters must be known here:
2. The identification system sends a response to the MODBUS master. This response includes
the content of the requested register. If an error occurs, the response contains an exception
code. A read/write command must be executed from the first address of the relevant channel.
Example:
In this example, the responses generated in the previous example are retrieved. The following
prerequisite must be fulfilled:
■
The example of the
write multiple registers
was executed successfully.
First step
The MODBUS master parameters must be configured:
Second step
A
read holding registers
MODBUS command must be executed. The contents of the register
indicate the response to the executed identification command
change tag
.
Note!
When all 3 steps have been completed successfully, LED 2 under the display must light up
green. If you then hold a type IPC03 data carrier in front of the reading head, the LED should
light up orange. If you wish to transfer an identification command to the identification system a
second time, the toggle bit must be inverted to enable the transfer of cyclic data to a PLC.
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 read:
Maximum 125d
Table 7.9
Parameters required for a request
Slave IP address:
Identification system IP address
Timeout time:
1000 ms
Device ID:
1
Start address:
2000d
Number of registers to be read:
12d
Table 7.10
MODBUS master parameters
