Moeller DF51 - Function Names and Numbers

Serial interface (Modbus)
10/05 AWB8230-1541GB
152
The protocol (Modbus) frame has the following structure:
• Header (non-operative mode)
• Slave address
• Function code
•Data
•Error check
• Trailer (non-operative mode)
Structure of request
Slave address
• Here the slave address (1 to 32) of the recipient frequency
inverter is entered. (Only the frequency inverter with this
address can respond to the request).
• Slave address 0 is used for broadcasting (sending a message to
all bus stations). In this mode no single station can be
addressed and slaves can not respond.
Data format
The DF51 frequency inverters’ data format corresponds to the
Modbus data format:
Function names and numbers
Table 41: Specified function of the DF51:
Error check
Modbus RTU uses cyclic block testing, also called CRC (cyclic
redundancy checking) to check the data transfer for errors. The
CRC code is a 16-bit data word consisting of 8-bit data blocks of
any length. The CRC checksum is generated with generated
polynomial CRC-16 (X16 + X15 + X2 + 1).
Non-operational mode (header and trailer)
The latency is the time between the request from the master and
the response from the frequency inverter (slave), i.e. the time in
which the changeover between transmission and reception takes
place. At least 3.5 characters (24-bit rest time) of latency are
always required. If the time is shorter, is the frequency inverter
does not respond. The actual latency is the sum of the rest time
(3.5 characters) and PNU C078 (waiting time until fault message).
Figure 157:Error checking
t
L
: Latency (waiting time plus PNU C078)
h
The frequency inverter (slave) sends a response only if it
has previously received a request from the master.
Request
PLC (host, master)
Response
Frequency inverter
DF51 (slave)
t
t
L
Data name
Description
Coil (bit) 1-bit binary data, which can be allocated and
changed
Holding register
(word)
16-bit binary data, which can be allocated
and changed
h
In this manual, the following standard English names and
designations for Modbus are used
Function code Function Modbus standard name Maximum data
size (vavailable
bytes per
message)
Maximum number
of data elements
per message
dec hex
101Read variable bit (coils) Read multiple coil status 4 32 coils (in bits)
303Read word variables (register) Read multiple holding registers 4 4 registers (in bytes)
505
Write a bit variable (coil) Force single coil 1 1 coil (in bits)
606
Write a word variable (register) Force single register 1 1 register (in bytes)
808
Connection test Loop back diagnostic test (00: return
query data)
– –
15 0F Write multiple bit variables (coils) Force multiple coil 4 32 coils (in bits)
16 10 Write multiple word variables (register) Force multiple registers 4 4 registers (in bytes)
Data elements: 1 byte = 8 bit