Service manual

EXTERNAL SERIAL CONTROL PROTOCOL
B-2
April 2001
Part No. 001-9800-203
Table B-2 Message Format
Sync Source Address Destination Address Opcode Data Checksum Escape
1 byte 1 byte 1 byte 1 byte 0-n bytes 1 byte 1 byte
0xba 0x0? 0x0? 0x?? 0x?? 0x?? 0x7e
Sync - The first character of each message.
Source Address - The originating
device.
Destination Address - The intended receive device (only the subscriber unit may use 0xff to broadcast messages).
Opcode - Indicates what message is being sent.
Data - Opcode data, if needed.
Checksum - Two’s complement of the sum of the original
characters in the message excluding initial SYNC, final
ESCape, and inserted DLE/replacement characters. The checksum is implemented as a single byte, with all
overflow ignored.
Escape - The last character of each message.
B.2.2 FRAME ENCODING/DECODING
EXAMPLES
No Embedded Special Characters
Sample Data Packet:
Formatted data string:
0xba, 0x01, 0x02, 0x37, 0x02, 0xc4, 0x7e
Embedded Sync Character
Sample Data Packet:
Formatted data string
:
0xba, 0x01, 0x02, 0x37, 0x10, 0x00, 0x0c, 0x7e
Embedded Escape Character
Sample data packet:
Formatted data string
:
0xba, 0x01, 0x02, 0x37, 0x10, 0x01, 0x48, 0x7e
Embedded DLE Character
Sample data packet:
Formatted data string
:
0xba, 0x01, 0x02, 0x37, 0x10, 0x02, 0xb6, 0x7e
Multiple Embedded Characters
Sample data packet:
Source
Address
Destination
Address
Opcode Data
0x01 0x02 0x37 0x02
Source
Address
Destination
Address
Opcode Data
0x01 0x02 0x37 0xba
Source
Address
Destination
Address
Opcode Data
0x01 0x02 0x37 0x7E
Source
Address
Destination
Address
Opcode Data
0x01 0x02 0x37 0x10
Source
Address
Destination
Address
Opcode Data
0x01 0x02 0x37 0x10, 0x33, 0xFF,
0xba, 0xba