December 2007
Page 30
90-005-0003 Rev X01
50 Watt Ka Feedmount BUC User Manual
21 0x15
NAK Negative
Acknowledge
0x30
to
0x39
Address
One byte, typically in the range 0x30 to 0x39,
but can be any value other than STX, ETX,
ACK or NAK. Must match the value configured
into the M&C unit or the message is ignored
0x30
to
0xF0
Command
One byte, typically in range 0x30 to 0xF0, but
can be any value other than STX, ETX, ACK, or
NAK
Data
Up to 570 bytes of ASCII characters
Checksum
One byte containing the XOR of all previous
bytes including STX and ETX
Echo
Address
Echo
Command
Response to Errors:
•
If the address does not match, the M&C will not respond.
•
If the checksum is invalid, the M&C will not respond.
ASCII Encoding of Binary Data:
All binary data sent and received by the M&C unit is encoded into ASCII characters.
If a communication protocol allows unrestricted binary data, it is impossible to
designate a unique start, stop, ack or nak byte. Since the data payload of a packet
can contain bytes of any value, you are never sure if a byte is a control code, or
part of the payload. If a communication is corrupted, and the receiver loses track of
where it is in a message, there is no reliable way to guarantee resynchronization. In
the worst case, depending on the data payload, the communication might never
recover synchronization.
By following this rule, the start, stop, ack, and nak codes are guaranteed to never
be present in the data payload.
All binary data is encoded in hex ASCII in Intel byte order. Intel byte order is also
known as little endian, since the list significant byte is first in memory.
