EverFocus EDSR-1600 Instruction Manual page 63

2-1. The format of message packet is as follows:
Length Byte (Prefix: 0x86, 0x87, or 0x88 ..... )
Receiver ID high byte
Receiver ID low byte
Opcode Byte
Data Byte1
Data Byte2
Data Byte3
Checksum Byte
2-2. Length Byte
This Length Byte is also a prefix. Bit7 must be 1.
EX:
Appendix C: Serial Interface Specifications
0x87 ==> this packets has 7 bytes length. ( not included Length byte itself )
58