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4-4
Chapter 4. CPL Communication
•
If “0” is set on a slave station, its RS-485 communication function will be
disabled. To enable a station to communicate, be sure to set its address to “1”
or above.
•
Do not send a command addressed to device address “0” from the master
station.
z
Subaddress
Description : Always the same for this device. Be sure to set the subaddress
"00" (30H, 30H), the same format as the device address.
z
Device type code
Description : Only the hex character codes for "X" (58H) or "x" (78H) can be
used on this device.
z
ETX (End of Text)
Role
: This indicates the end of the application layer.
Description : Always 03H.
z
Checksum
Role
: The checksum is used to check whether the message changed due
to some problem (e.g., electrical noise) during communication.
Description : The hexadecimal codes for two characters.
· How to create a checksum
(1) Add all the values of each byte of the message from STX to
ETX.
(2) Take the two's complement of the sum.
(3) Convert the result to character codes.
Example: The instruction message described above is used in the following
example:
(1) Add all the character codes from STX to ETX.
The lowest 1 byte of the calculation result is 76H.
(2) Take the two's complement of the addition result.
The result is 8AH.
(3) Replace the characters of the result with their hexadecimal character
codes. The result is used for the checksum.
"8A" becomes 38H and 41H.
Note
•
(for the example of conversion to character
codes)
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