SATO MB410i Operator's Manual page 56

Unit 4: Operation and Configuration
The block number starts from 1, and when counting to 255, the number goes back to 0 again. If
the block number is [01h], complement of block number becomes [FEh]. In the main data, the
section of data by 128 bytes is stored. SUM is the check sum computed from 128 bytes of main
data.
NOTE: The above method is the XMODEM (check sum) option.
Select this option in the XMODEM settings on the host side.
When downloading data, the format is such that the first 16 bytes are used as header information
and the rest is considered as data. The header information is divided thus: code (4 bytes), start
address (4 bytes), file size (4 bytes), and reserved area (4 bytes). The remaining optional data is
to be stored in Flash ROM.
The basic sequence of XMODEM is to transfer data blocks by individually checking response
blocks. NAK (15h) transmission by the receiving end initiates the sequence, and the sending end
sends the first data block after receiving NAK. The receiving end receives and checks this data
block, and then returns ACK (06h) in case of no error or NAK (15h) in case of an error. The
sending end sends the next block when receiving ACK, and resends the same block when
receiving NAK. This process repeats to the first block. EOT (04h) is sent from the sending end to
receiving end at the end of all data transmission. After receiving EOT (04h), the receiving end
returns ACK to terminate the sequence.
Page 4-18 PN 9001190C MB400i/MB410i Operator Manual