74
4-1 Command data packet format
The general packet format is as following
:
Length
Opcode
Status
Data
Checksum
Notice:
Opcode is the abbreviation about Operation code.
Table 4-2 lists the descriptions of fields that occur in all messages. This description is repeated for each
opcode. For messages that use the data field, the specific type of data is described in that field in later
sections.
Table 4-2 Field descriptions
Field
name
Type
Sub-Field
Description
Length
1 byte
Length
Length of message not including
the check sum bytes. Maximum
value is 0xFF.
Opcode
1 byte
See table 4-1 for details
Identifies the command being
sent.
Status
Bit0
Retransmit
0 = First time packet is sent
1 = Subsequent transmission
attempts
Bit5-1
Parameter property
(use for parameter requesting and
parameter transmission)
Bit6
Change type
(apply to parameter transmission)
0 = Temporary change
1 = Permanent change
Bit7
Command source
1:Command is from the host.
0:Command is from the scanner
Data
Variable number
of bytes
See individual sections for details
Checksum
2 bytes
2’s complement sum of message
contents excluding checksum
Checksum of message formatted
as High-Byte Low-Byte
Note:
The checksum is a 2 byte checksum and must be sent as High-Byte followed by Low-Byte.
Checksum = 0x10000 – Length - Opcode - Status – Data.
