Panasonic KX-T336 System Reference Manual page 1588

Address Area
STX
SOH
Data Area ETX
Transmission Format
SOH = Start of header
STX = Start of text
Address = System data address
(Is system address is "FFFFF h", it
would be software version)
(Binary data)
The number of byte = 1 to 256 (Binary data)
Data area = System data (Binary data)
Checksum = Address + The number of bytes +
data
ETX = End of text
EOT = End of data transfer
The number
of byte
STX Address Area
17-B-3
Data Area
The number
of byte
ETX EOT