1)header
code consisting of one byte for frame synchronization.
the frame header send from the master machine is termed the command header.
the frame header send from the slave machine is termed the return header.
the command header byte is fixed as fallow.
1st: f0h (base 16)
the return header byte is fixed as fallow.
1st: fch (base 16)
2)id number
the equipment id number is composed of 8 bits
the id of se800 : 21h (base 16)
3)length
the length is the sum of bytes from the header to the end.
it is composed of 8 bits.
6h (base 16) [ length [= 80h(base 16)
4) data
data block used by application layer.
refer to section 3.
5) checksum
the 8 bits checksum is obtain from header to the last data,
then convert to two numeric ascii code.
checksum=header+id+legth+data0+data1+…+data_last
chksum_l=(low nibble of checksum) + 30h
chksum_h=(high nibble of checksum) + 30h
6) end
the end byte are fixed to ffh(base 16).