Alcorn Mcbride Digital Video Machine HD, User Manual

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50 Ethernet Control
Control Message Format
The control source will send a UDP packet that contains an Information Station
Control Message as the User Data in the packet. A UDP Control Message is
comprised of a few bytes needed specifically for AMINet and some Command
bytes. The Command simply needs to contain an Addressed Pioneer / AMI
protocol command. For example, An Information Station Control Message
containing the Command bytes 7@?V<CR> would cause the Information Station
on the network with Unit ID 7 to send back a UDP packet containing its version
information. Please see the
Serial Command Summary section
for detailed
information about the rest of the command set.
The basic format of an Information Station Control Message is as follows:
0xF1 0x01 0x04 <Pioneer / AMI Command> <Checksum> 0xF2
The only bytes that change from message to message are the Command bytes
and the Checksum. The command corresponds exactly to an Addressed Pioneer
/ AMI serial command.
Control Message Checksum
The Checksum is the summation of the hexadecimal value of all of the bytes in
the Control Message except the first byte (0xF1), the last byte (0xF2) and of
course the Checksum itself. The value of the checksum may easily increase to a
value that cannot be represented by one byte. This situation calls for what we
call number expansion.
If the value of the Checksum is between 0x00 and 0xF9 (0-249), the value is
represented in only 8 bits (1 byte). If the value is between 0xFA and 0xFFFF
(250-65535), the value is represented in 16 bits (2 bytes) and is preceded by
0xFF to signify the number has been expanded to 16 bits. If the value is between
0x10000 and 0xFFFFFF (65536-16777215), the value is represented in 24 bits
(3 bytes) and is preceded by 0xFE to signify the number has been expanded to
24 bits. The following example shows a Control Message with an expanded
Checksum.
0xF1 0x01 0x04 5 5 @ R J <CR> 0xFF 0x01 0x58 0xF2
The value of the checksum is calculated by adding the hexadecimal values of
each byte preceding it except the first byte (0xF1) as follows: