Astraada DRV-24 frequency inverters Communication protocol
95
ADDR
Communication address: 0~247(decimal system)(0 is the
broadcast address)
CMD
03H:read slave parameters
06H:write slave parameters
DATA (N-1)
…
DATA (0)
The data of 2*N bytes are the main content of the
communication as well as the core of data exchanging
CRC CHK low bit
Detection value:CRC (16BIT
）
CRC CHK high bit
END
T1-T2-T3-T4(transmission time of 3.5 bytes)
7.2.2.2 RTU communication frame error checkout
Various factors (such as electromagnetic interference) may cause error in the data transmission. For
example, if the sending message is a logic “1”,A-B potential difference on RS485 should be 6V, but in
reality, it may be -6V because of electromagnetic interference, and then the other devices take the
sent message as logic“0”. If there is no error checkout, the receiving devices will not find the
message is wrong and they may give incorrect response which cause serious result. So the checkout
is essential to the message.
The theme of checkout is that: the sender calculate the sending data according to a fixed formula,
and then send the result with the message. When the receiver gets this message, they will calculate
anther result according to the same method and compare it with the sending one. If two results are
the same, the message is correct. If not, the message is incorrect.
The error checkout of the frame can be divided into two parts: the bit checkout of the byte and the
whole data checkout of the frame (CRC check).
Bit checkout of the byte
The user can select different bit checkouts or non-checkout, which impacts the check bit setting of
each byte.
The definition of even checkout: add an even check bit before the data transmission to illustrate the
number of “1” in the data transmission is odd number or even number. When it is even, the check
byte is “0”, otherwise, the check byte is”1”. This method is used to stabilize the parity of the data.
The definition of odd checkout: add an odd check bit before the data transmission to illustrate the
number of “1” in the data transmission is odd number or even number. When it is odd, the check byte
is “0”, otherwise, the check byte is”1”. This method is used to stabilize the parity of the data.
For example, when transmitting “11001110”, there are five “1” in the data. If the even checkout is
applied, the even check bit is “1”; if the odd checkout is applied; the odd check bit is “0”. The even and
odd check bit is calculated on the check bit position of the frame. And the receiving devices also carry
out even and odd checkout. If the parity of the receiving data is different from the setting value, there
is an error in the communication.
CRC check
The checkout uses RTU frame format. The frame includes the frame error detection field which is
based on the CRC calculation method. The CRC field is two bytes, including 16 figure binary values. It is
added into the frame after calculated by transmitting device. The receiving device recalculates the CRC
of the received frame and compares them with the value in the received CRC field. If the two CRC
values are different, there is an error in the communication.
During CRC, 0*FFFF will be stored. And then, deal with the continuous 6-above bytes in the frame and
the value in the register. Only the 8Bit data in every character is effective to CRC, while the start bit,
the end and the odd and even check bit is ineffective.
The calculation of CRC applies the international standard CRC checkout principles. When the user is
editing CRC calculation, he can refer to the relative standard CRC calculation to write the required CRC
Summary of Contents for AS24DRV4075
Page 1: ...Operation Manual Astraada DRV 24 Frequency inverters ...
Page 2: ......
