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2. The Barco Projection Protocol
Character strings can be formatted in two ways:
• C-style format
An array of o ne or more characters which is terminated by a NULL character (0x00). The position of the NULL character
determines the length of the string.
Example: ’f’ ’o’ ’o’ ’ ’ ’b’ ’a’ ’r’ 0x00
• Pascal-style format
An array of one or more characters which is started (the first byte) with the length of the string. Therefore, Pascal-style strings
are limited to 255 characters.
Example: 0x07 ’f’ ’o’ ’o’’’’b’’a’’r’
ANSI
American National S tandards Institute
Data words
A data word is a value which consists of m ultiple bytes. Data words are formatted in big endian.
How to calculate the value of a data word?
Example of a 4-byte value: 0x01 0x20 0x50 0x30
=(0x01 * 256^3) + (0x20 * 256^2) + (0x50 * 256^1) + (0x30 * 256^0)
= (1 * 16777216) + (32 * 65536) + (80 * 256) + (48 * 1)
= 16777216 + 2 097152 + 20480 + 48
= 18894896
msb
The most significant byte, is the byte with th e greatest w eight (value).
lsb
The less significant byte, is the byte with the s mallest weight (value).
Big endian
When the firstbyteofadatawordisthemsb and the last byte is the lsb, the data word is in big endian.
Negative values
The two’s complement (2-com plement) system is used for the representation of negative values.
Acknowledgement (ACK and NACK)
If a c omm and is received, the receiver will check the v alidity and correctness o f the com m and before processing it. If the command
is understood, the receiver will first acknowledge the command before doing the actual processing of the comm and. An AC K (AC-
Knowledge) is sent when these conditions are met:
• The command format is correct
• The command and its parameters are valid
• The checksum is correct
When these conditions are not met, a NACK (Not ACK nowledge) is sent.
ACK NACK
Byte 1
0x00 0x00
Byte 2
0x06 0x15
When the sender receives a NACK message, it is up the s ender to decide what shou ld happen next: retry sending the command or
discard the command.
Acknowledgements are not used in multicast com mun ication.
6 R5905746 COMMAND CATALOG 06/01/2014