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ALERT
BURST
ACK
ALERT
BURST
NAK
Data Packets
A Data Packet consists of the actual data being
sent to another node. It is sent by the following
sequence:
• An ALERT BURST
• An SOH (Start Of Header--ASCII code 01H)
• An SID (Source ID) character
• Two (repeated) DID (Destination ID)
characters
• A single COUNT character which is the 2's
complement of the number of data bytes to
follow if a short packet is sent, or 00H
followed by a COUNT character if a long
packet is sent
• N data bytes where COUNT = 256-N (or 512-
N for a long packet)
• Two CRC (Cyclic Redundancy Check)
characters. The CRC polynomial used is:
X
16
+ X
15
+ X
2
+ 1.
A
L
E
R
T
B
U
R
S
T
S
O
H
S
I
D
D
I
D
D
I
D
C
O
U
N
T
d
a
t
a
d
a
t
a
C
R
C
C
R
C
Acknowledgements
An Acknowledgement is used to acknowledge
reception of a packet or as an affirmative
response to FREE BUFFER ENQUIRIES and is
sent by the following sequence:
• An ALERT BURST
• An ACK (ACKnowledgement--ASCII code
86H) character
Negative Acknowledgements
A Negative Acknowledgement is used as a
negative response to FREE BUFFER
ENQUIRIES and is sent by the following
sequence:
• An ALERT BURST
• A NAK (Negative Acknowledgement--ASCII
code 15H) character