COM20022V-HT Ver la hoja de datos (PDF) - SMSC -> Microchip

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COM20022V-HT

10Mbps ARCNET controller with 2Kx8 on-board RAM

SMSC -> Microchip 

transmit a message can be precisely determined.

The line idles in a spacing (logic "0") condition. A

logic "0" is defined as no line activity and a logic

"1" is defined as a negative pulse of 50nS

duration. A transmission starts with an ALERT

BURST consisting of 6 unit intervals of mark (logic

"1"). Eight bit data characters are then sent, with

each character preceded by 2 unit intervals of

mark and one unit interval of space. Five types of

transmission can be performed as described

below:

Invitations To Transmit

An Invitation To Transmit is used to pass the

token from one node to another and is sent by the

following sequence:

!" An ALERT BURST

!" An EOT (End Of Transmission: ASCII code

04H)

!" Two (repeated) DID (Destination ID)

characters

ALERT

EOT

DID

DID

BURST

Free Buffer Enquiries

A Free Buffer Enquiry is used to ask another node

if it is able to accept a packet of data. It is sent by

the following sequence:

!" An ALERT BURST

!" An ENQ (ENQuiry: ASCII code 85H)

!" Two (repeated) DID (Destination ID)

characters

!" 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:

X16 + X15 + X2 + 1.

ALERT

SOH SID DID DID COUNT data

BURST

data CRC CRC

ALERT

ENQ

DID

DID

BURST

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

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