SIGNATURE
B
US
P
ROTOCOL
M
ASTER
D
OCUMENT
Revised 2-24-98
Page 6 of 20
The Command Modifier is a byte that distinguishes what type of command
is being sent.
HEX
Command Type
01
Action request
02
Action response
Provides additional information required by the Command byte.
The Command byte is the action that is desired.
The Data Length is a word representing the total number of bytes
(including Command Modifier and Command bytes, but not the Data
Length byte itself or the Checksum byte) in the data portion of the
message. Minimum length is 02
h
.
Source
Device Type
Target
Device Type
Target
Unit ID
Source
Unit ID
Command
Modifier
Data
Length
Preamble
Byte
Command
Byte
Data
Byte(s)
Checksum
Byte
Source
Device Type
Target
Device Type
Target
Unit ID
Source
Unit ID
Command
Modifier
Data
Length
Preamble
Byte
Command
Byte
Data
Byte(s)
Checksum
Byte
Source
Device Type
Target
Device Type
Target
Unit ID
Source
Unit ID
Command
Modifier
Data
Length
Preamble
Byte
Command
Byte
Data
Byte(s)
Checksum
Byte
The Source Unit ID is a byte that distinguishes which unit of a given type
the message is coming from (i.e. CD player #1 versus CD player #2). The
Unit ID is set in the menu system of the unit that the message is coming
from, default = 01
h.
If you are using more than one of any given unit, you
will need to modify this byte.
Source
Device Type
Target
Device Type
Target
Unit ID
Source
Unit ID
Command
Modifier
Data
Length
Preamble
Byte
Command
Byte
Data
Byte(s)
Checksum
Byte
Provides additional information required by the Command byte.
The Data bytes consist of information that is required to complete the
Command. The Data bytes are detailed throughout the rest of this
document.
Source
Device Type
Target
Device Type
Target
Unit ID
Source
Unit ID
Command
Modifier
Data
Length
Preamble
Byte
Command
Byte
Data
Byte(s)
Checksum
Byte
Provides additional information required by the Command byte.
The Checksum is a byte whose value confirms/voids the validity of a
received message. It is computed by adding up all of the bytes Preamble
through the last Data byte, and then taking the 1s complement of the lower
eight bits of that sum (i.e. add up all the bytes, truncate to eight bits, and
invert each of the bits). If the result equals 7E
h
, add 01
h
.
See the page 7
for an example.
Source
Device Type
Target
Device Type
Target
Unit ID
Source
Unit ID
Command
Modifier
Data
Length
Preamble
Byte
Command
Byte
Data
Byte(s)
Checksum
Byte
