COM20019I Datasheet, PDF (14/65 Pages) SMSC Corporation – Low Cost ARCNET(ANSI 878.1) Controller with 2k X 8 On-Board RAM

Low Cost ARCNET (ANSI 878.1) Controller with 2K x 8 On-Board RAM
ƒ An ALERT BURST
ƒ An SOH (Start Of Header--ASCII code 01H)
ƒ An SID (Source ID) character
ƒ Two (repeated) DID (Destination ID) characters
ƒ 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.
ƒ N data bytes where COUNT = 256-N (or 512-N for a long packet)
ƒ Two CRC (Cyclic Redundancy Check) characters. The CRC polynomial used is: X¹⁶ + X¹⁵ + X² + 1.
ALERT
SOH SID DID DID COUNT data
BURST
data CRC CRC
4.6.4 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:
ƒ An ALERT BURST
ƒ An ACK (ACKnowledgement--ASCII code 86H) character
ALERT BURST
ACK
4.6.5 Negative Acknowledgements
A Negative Acknowledgement is used as a negative response to FREE BUFFER ENQUIRIES and is sent
by the following sequence:
ƒ An ALERT BURST
ƒ A NAK (Negative Acknowledgement--ASCII code 15H) character
ALERT BURST
NAK
Rev. 04-15-05
Page 14
DATASHEET
SMSC COM20019I