com20020-5 Standard Microsystems Corp., com20020-5 Datasheet - Page 11

• Manufacturer Part Number: com20020-5
• Description: Com20020-5 Ulanc Universal Local Area Network Controller With 2k X 8 On-board Ram
• Manufacturer: Standard Microsystems Corp.

Data Packets
A Data Packet consists of the actual data being
sent to another node. It is sent by the following
sequence:
Acknowledgements (ACK)
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 SOH (Start Of Header--ASCII code 01H)
An SID (Source ID) character
Two
An ALERT BURST
An ACK (ACKnowledgement--ASCII code
characters
86H) character
ALERT
BURST
(repeated)
DID
ACK
(Destination
ID)
11
Negative Acknowledgements (NAK)
A Negative Acknowledgement is used as a
negative
ENQUIRIES and is sent by the following
sequence:
A single COUNT character which is the 2's
N data bytes where COUNT = 256-N (or 512-
Two
An ALERT BURST
A NAK (Negative Acknowledgement--ASCII
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 for a long packet)
characters. The CRC polynomial used is:
X
code 15H) character
16
+ X
CRC
15
response
+ X
ALERT
BURST
2
(Cyclic
+ 1.
to
NAK
Redundancy
FREE
BUFFER
Check)