136
COMMISSIONING MANUAL
POWERDRIVE MD
Variable speed drive
OPERATION WITH MODBUS RTU
LEROY-SOMER
3871 en - 2011.05 / h
10.40
: Status word
6.4 - MODBUS RTU
6.4.1 - General
The MODBUS RTU protocol is a master-slave type protocol
(a single master per network).
Note:
If the CT Comms cable is used, the baud rate is limited
to 38400 baud.
6.4.2 - Description of exchan
g
es
Exchanges are initiated by the master, which sends its
request: if the slave concerned has understood it, it sends its
response. Each frame (question or response) contains four
types of data:
- The address of the slave concerned which receives the
question frame (master request) or the address of the slave
which sends the response frame (encoded in one byte)
- The function code which selects a command (read or write
words, bits etc) for question and response frames (encoded
in one byte)
- The data field containing the parameters relating to the
command (encoded in "n" bytes)
- The frame CRC, calculated over sixteen bits, which is used
to detect transmission errors.
The frame is terminated with a minimum silence period,
equivalent to the transmission time for 3.5 characters (e.g. at
19200 baud, the silence period must be at least 1/19200 x
11 bits x 3.5, i.e. 2 ms). This silence period indicates the end
of the message, and the slave can start to process the
transmitted data.
All data is encoded in hexadecimal format.
All master requests will lead to a response from a single
slave. The slave will respond within the maximum allotted
time (the minimum response time is never less than the
silence period).
See diagram below.
Status
word bits
10.40
Correspondin
g
parameters
Drive status
0
10.01
Drive healthy
1
10.02
Drive active
2
10.03
Zero speed
3
10.04
Running at minimum speed
4
10.05
Below set speed
5
10.06
At speed
6
10.07
Above set speed
7
10.08
Nominal load reached
8
10.09
Drive out at current limit
9
10.10
Drive regenerating
10
10.11
Braking IGBT active
11
10.12
Braking resistor alarm
12
10.13
Direction commanded
13
10.14
Direction running
14
10.15
Mains loss
Description
Characteristics
Normal physical layer for
multi-drop operation
2-wire RS485
Bit stream
Standard UART asynchronous
symbols with Non-Return to
Zero (NRZ)
Symbol
Each symbol consists of:
1 start bit
8 data bits (least significant bit
transmitted first)
1 or 2 stop bits according to
11.27
Baud rate
300, 600, 1200, 2400, 4800,
9600, 19200, 38400, 57600,
115200 baud
Slave
Function
Message data
CRC
Interval
address
code
16-bit
silence
Master request
Master request
Frame detection
Frame processing
by the slave
Minimum silence period
Slave response
time
Slave response
Minimum silence period