COM90C66 datasheet(11/76 Pages) SMSC

11 / 76 page

transmitted every 4.4 µS and the time to 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 200 nS duration.

A transmission starts with an ALERT BURST

consisting of six unit intervals of mark (logic "1").

Eight-bit data characters are then sent with each

character preceded by two 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

04 HEX)

• Two

(repeated)

DID

(Destination

IDentification) characters

ALERT

BURST

EOT

DID

Free Buffer Enquiries

A Free Buffer Enquiry is used to ask another

node if it is able to accept a packet of data and

is sent by the following sequence:

• An ALERT BURST

• An ENQ (ENQuiry--ASCII code 85 HEX)

• Two

(repeated)

DID

(Destination

IDentification) characters

Data Packets

A Data Packet consists of the actual data being

sent to another node and is sent by the following

sequence:

• An ALERT BURST

• An SOH (Start Of Header--ASCII code 01

HEX)

• An SID (Source IDentification) character

• Two

(repeated)

DID

(Destination

IDentification) characters

• A single COUNT character which is the 2's

complement of the number of data bytes to

follow if a short packet is being sent or 00

HEX followed by a COUNT character which

is the 2's complement of the number of data

bytes to follow if a long packet is being 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

+ X

+ 1.

ALERT

BURST

ENQ

DID

ALERT

BURST

SOH

SID

DID

COUNT

data

CRC

COM90C66 Datasheet(PDF) 11 Page - SMSC Corporation

COM90C66 Datasheet(HTML) 11 Page - SMSC Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76

Datasheet Download

Link URL