Operation Proline Promag 53 MODBUS RS485
64 Endress+Hauser
5.5.3 MODBUS function codes
The function code determines which read, write and test operations should be executed by means
of the MODBUS protocol. The measuring device supports the following function codes:
!
Note!
• Broadcast messages are only permitted with function codes 06, 16 and 23.
• The measuring device does not differentiate between function codes 03 and 04. These codes have
the same result.
5.5.4 Maximum number of writes
If a nonvolatile device parameter is modified via the MODBUS function codes 06, 16 or 23, this
change is saved in the EEPROM of the measuring device.
The number of writes to the EEPROM is technically restricted to a maximum of 1 million. Attention
must be paid to this limit since, if exceeded, it results in data loss and measuring device failure. For
this reason, avoid constantly writing nonvolatile device parameters via the MODBUS!
Function
code
Name in accordance
with
MODBUS specification
Description
03 READ HOLDING
REGISTER
Reads one or more registers of the MODBUS slave.
1 to a maximum of 125 consecutive registers
(1 register = 2 byte) can be read with a telegram.
Application:
For reading measuring device parameters with read and write access,
such as reading the volume flow.
04 READ INPUT REGISTER Reads one or more registers of the MODBUS slave.
1 to a maximum of 125 consecutive registers
(1 register = 2 byte) can be read with a telegram.
Application:
For reading measuring device parameters with read access, such as
reading the measured values (volume flow, totalizer value etc.).
06 WRITE SINGLE
REGISTERS
Writes a slave register with a new value.
Application:
For writing just one measuring device parameter, such as writing the
batch quantity or resetting the totalizer.
!
Note!
Function code 16 is used for writing several registers by means of just
one telegram.
08 DIAGNOSTICS Checks the communication connection between the master and slave.
The following "diagnostics codes" are supported:
• Sub-function 00 = Return query data (loopback test)
• Sub-function 02 = Return diagnostics register
16 WRITE MULTIPLE
REGISTERS
Writes several slave registers with a new value.
A maximum of 120 consecutive registers can be written with a
telegram.
Application:
For writing several measuring device parameters, such as writing the
batch quantity and resetting the totalizer.
23 READ/WRITE
MULTIPLE REGISTERS
Simultaneous reading and writing of 1 to max. 118 registers in a
telegram. Write access is executed before read access.
Application:
For writing and reading several measuring device parameters, such as
writing the batch quantity and the compensation quantity and reading
the totalizer value.
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