Modbus Function Codes; Maximum Number Of Writes - Endress+Hauser Cubemass DCI Operating Instructions Manual

Cubemass DCI MODBUS RS485
!
Endress+Hauser
5.4.3

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:
Function Name in accordance
code with
MODBUS specification
03 READ HOLDING
REGISTER
04 READ INPUT REGISTER
06 WRITE SINGLE
REGISTERS
08 DIAGNOSTICS
16 WRITE MULTIPLE
REGISTERS
23 READ/WRITE
MULTIPLE REGISTERS
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.
5.4.4

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!
Description
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 batch quantity.
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 (mass flow, temperature etc.).
Writes a single 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.
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
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.
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 correction quantity and reading the
totalizer value.
Operation
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