Checking For Communication Frame Errors - INVT DA180-S2R8SG0 Operation Manual

DA180 series basic AC servo drive
Write MSB of data start address
Write LSB of data start address
MSB of data count (in word)
LSB of data count (in word)
CRC CHK LSB
CRC CHK MSB

8.2.5 Checking for communication frame errors

Checking for communication frame errors consists of bit checking (that is, parity checking) for bytes
and entire-data checking (that is, CRC or LRC) for frames.
8.2.5.1 Bit checking for bytes
You can select different methods or even no checking based on your requirements, which affects the
check bit setting of each byte.
Even parity: An even parity bit is added before data transmission, indicating the number of 1 in the
transmitted data is even or odd. If the number is even, the parity bit is 0. Otherwise, the parity bit is 1.
Odd parity: An odd parity bit is added before data transmission, indicating the number of 1 in the
transmitted data is even or odd. If the number is odd, the parity bit is 0. Otherwise, the parity bit is 1.
Example: The number 11001110 is to be transmitted: If even parity is used, the even parity bit is 1; if
odd parity is used, the odd parity bit is 0. During transmission, the even/odd parity bit is placed in the
parity check position after calculation.
8.2.5.2 Cyclical Redundancy Check (CRC)
An RTU frame includes the domain for checking for errors in the entire frame using the CRC method.
This CRC domain consists of two bytes, including 16-bit hexadecimals. It is added to the frame after
being calculated by the sender. The receiver recalculates the CRC in the received frame and
compares it with the value in the received CRC domain. If the CRC values are different, a
transmission error occurred.
Before CRC, 0xFFFF is stored to the register, and then a process is invoked to compare the
successive 6 bytes or more with the values in the register. Only when the 8-bit data in each character
is valid to CRC, the start bit, stop bit, and parity bit are invalid.
During CRC generation, each 8-bit character has an independent exclusive or relationship with
register content. The comparison result moves towards the LSB direction, and 0 is padded to the
Table 8-5 Slave-node response message
START
ADDR
CMD
END
T1-T2-T3-T4 (3.5-byte transmission time)
T1-T2-T3-T4 (3.5-byte transmission time)
-246-
Communication
01H
10H
03H
F2H
00H
02H
E0H
7FH