BenQ PB6200 - Manual (Page 64)

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The Packet Header size is fixed at seven bytes (Intel byte ordering is used). The following code fragments are taken
from these source files
The Packet Header definition is shown below:
typedef struct
{
BYTE ePacketType; // type of the payload
WORD nPacketSize; // size of the payload
WORD nCRCPacket; // CRC for the entire packet
} PACKET_HEADER;
Magic Number
The Magic Number is a fixed value that is used to insure packet alignment if there are partial packets received or
bytes lost. The Magic Number is a WORD in length (2 bytes). The Magic Number value is 0xEFBE. Because Intel
byte ordering is used, the ls-byte of the word is sent first (byte0 = 0xBE), then the ms-byte (byte1 = 0xEF).
Packet Type
The Packet Type (ePacketType) is a BYTE in length number that defines the type of data in the packet. The following
entries are valid packet typess:
Table 4
Packet
Types
Packet Payload Size
The Packet Payload Size (nPacketSize) is a BYTE that defines the size of the Payload portion of the packet. If the
packet contains only header information, this is zero. Therefore, the total byte count of any packet = nPacketSize plus
7 (since the Packet Header is seven bytes long).
Packet Checksum (CRC)
Each packet is CRC’ed using the tables later in this document. This number is the CRC value for the complete packet
including the Packet Header and Packet Payload. The CRC is calculated with the nCRCPacket value initialized to
zero.
Packet Type Name Packet Type
Number
Description
pt_INVALID 0 Invalid Packet Type
RESERVED 1 RESERVED
pt_EVENT 2 Host can send any event defined in BenQ PB6XXX
software.
pt_OPERATION 3 Host can send any operation defined in BenQ PB6XXX
software.