Epson GT-6500 EN - Manual (Page 65)

Block data structure
Block data consists of a 6-byte information block followed by n lines
of image data (n is the value of the line counter in the information
block).
You specify block data transfer with the ESC d (set line counter)
command. By sending multiple lines of data at once, you can shorten
the total data transfer time.
The information block size is fixed at 6 bytes. You can use the byte
counter and line counter in the information block to determine the
amount of data (number of bytes).
Information block
An information block is included in all data blocks; and provides
information on the beginning of the data block, the current state of the
scanner, and the length of the data that follows.
Header
This byte is always set to the STX code (02
H
), and indicates the
beginning of the data block.
Command Usage 2-27