COM90C66 datasheet(9/76 Pages) SMSC

9 / 76 page

PROTOCOL DESCRIPTION

NETWORK PROTOCOL

Communication on the network is based on a

token passing protocol.

Establishment of the

network configuration and management of the

network protocol are handled entirely by the

COM90C66's internal microcoded sequencer. A

processor or intelligent peripheral transmits data

simply

data

packet

and

its

destination ID into the RAM buffer and issuing a

command to enable the transmitter.

When the

COM90C66 next receives the token, it verifies

that

the

receiving

node

ready

first

transmitting

FREE

BUFFER

ENQUIRY

message. If the receiving node transmits an

ACKnowledge message, the data packet is

transmitted followed by a 16-bit CRC.

If the

receiving

node

cannot

the

packet

(typically its receiver is inhibited), it transmits a

Negative AcKnowledgement message and the

transmitter passes the token. Once it has been

established that the receiving node can accept

the packet and transmission is complete, the

receiving node will verify the packet.

If the

packet is received successfully, the receiving

node transmits an ACKnowledge message (or

nothing if it is received unsuccessfully) allowing

the transmitter to set the appropriate status bits

to indicate successful or unsuccessful delivery of

the packet.

An interrupt mask permits the

COM90C66 to generate an interrupt to the

processor when selected status bits become true.

Figure 1 is a flow chart illustrating the internal

operation of the COM90C66.

NETWORK RECONFIGURATION

A significant advantage of the COM90C66 is its

ability to adapt to changes on the network.

Whenever

new

node

activated

deactivated, a NETWORK RECONFIGURATION

is performed. When a new COM90C66 is turned

on (creating a new active node on the network),

or if the COM90C66 has not received an

INVITATION TO TRANSMIT for 840 mS, or if a

software reset occurs, the device causes a

NETWORK RECONFIGURATION by sending a

RECONFIGURE

BURST

consisting

eight

marks and one space repeated 765 times. The

purpose of this burst is to terminate all activity on

the network. Since this burst is longer than any

other type of transmission, the burst will interfere

with the next INVITATION TO TRANSMIT,

destroy the token and keep any other node from

assuming control of the line.

When any COM90C66 senses an idle line for

greater than 82 µS, which will only occur when

the token is lost, each COM90C66 starts an

internal timeout equal to 146 µS times the

quantity 255 minus its own ID. It also sets the

internally-stored NID (next ID representing the

next possible ID node) equal to its own ID. If the

timeout

expires

with

line

activity,

the

COM90C66

starts

sending

INVITATION

TRANSMIT with the Destination ID (DID) equal to

the currently-stored NID. Within a given network,

only one COM90C66 will timeout (the one with

the highest ID number).

After sending the

INVITATION TO TRANSMIT, the COM90C66

waits for activity on the line. If there is no activity

for 74.7µS, the COM90C66 increments the NID

value and transmits another INVITATION TO

TRANSMIT using the NID equal to the DID.

activity appears before the 74.7µS timeout

expires, the COM90C66 releases control of the

line.

During NETWORK RECONFIGURATION,

INVITATIONS TO TRANSMIT will be sent to all

256 possible IDs. Each COM90C66 on the

network will finally have saved a NID value equal

to the ID of the COM90C66 that it released

control to. At this point, control is passed directly

from one node to the next with no wasted

INVITATIONS TO TRANSMIT being sent to IDs

not on the network until the next NETWORK

RECONFIGURATION occurs.

When a node is

powered off, the previous node will attempt to

pass it the token by issuing an INVITATION TO

TRANSMIT. Since this node will not respond, the

previous node will timeout and transmit another

INVITATION TO TRANSMIT to an incremented

ID and eventually a response will be received.

COM90C66 数据表(PDF) 9 Page - SMSC Corporation

COM90C66 数据表(HTML) 9 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

数据表下载

链接网址

COM90C66 数据表(PDF) 9 Page - SMSC Corporation

COM90C66 数据表(HTML) 9 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

数据表 下载

链接网址

数据表下载