BenQ PB6100, PB6200 manual Packet Type Description

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 Type Name	Packet Type	Description
Packet		Number
Types	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.

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.

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