Savch S2800 Series, User Manual

Page: 93 / 112

ASCII assistant command information
90
START ‘:’
‘0’
ADDR
‘1’
‘0’
CMD
‘8’
‘0’
Sub-function code upper bit
‘0’
‘0’
Sub-function code lower bit
‘0’
‘1’
Date content upper bit
‘2’
‘A’
Date content lower bit
‘B’
LRC CHK Hi ‘3’
LRC CHK Lo ‘A’
END Hi CR
END Lo LF
H. Communication Frame Error-checking Method
The error-checking method of frame mainly includes two parts: bit checking of byte
(odd/even check) and whole data checking of frame (CRC checking and LRC checking).
I. Byte Checking
The user can select different byte checking method according to practical needs, and also
can select no checking which will affect the checking bit setting of every byte.
Even checking: adding an even bit before data transmission to express that the number of
"1" in transmitted data is odd or even. If the number is even, the checking bit is "0",
otherwise "1". It is used to keep the parity of data constant.
Odd checking: adding an odd bit before data transmission to express that the number of
"1" in transmitted data is odd or even. If the number is odd, the checking bit is "0",
otherwise "1". It is used to keep the parity of data constant.
For example, the transmitted data is "11001110". There are five "1" in it. If even checking is
adopted, its even parity checking bit is "1". If odd checking is adopted, its odd parity
checking bit is "0". In data transmission, the parity bit is put on the checking bit of frame
through computing. The receiving equipment also needs parity checking. If the parity of
received data is different from the preset situation, it indicates that there is communication
error received.