COM20020-5 Datasheet, PDF(39/58 Page) SMSC Corporation – Universal Local Area Network Controller with 2K x 8 On-Board RAM

English

English German Russian Spanish Italian Polish Chinese Japanese Korean French Portuguese	Language :

COM20020-5 Datasheet, PDF (39/58 Pages) SMSC Corporation – Universal Local Area Network Controller with 2K x 8 On-Board RAM

◁

MYRECON bit of the Diagnostic Status

occurrences of a logic "1" on the MYRECON bit

indicates that a problem exists with this node.

At that point, the transmitter should be disabled

so that the entire network is not held down

while the node is being evaluated.

The Duplicate ID (DUPID) bit is used before the

node joins the network to ensure that another

node with the same ID does not exist on the

network. Once it is determined that the ID in the

Node ID Register is unique, the software should

write a logic "1" to bit 5 of the Configuration

This allows the node to join the network.

The Receive Activity (RCVACT) bit of the

Diagnostic Status Register will be set to a logic

"1" whenever activity (logic "1") is detected on

the RXIN pin.

The Token Seen (TOKEN) bit is set to a logic "1"

whenever any token has been seen on the

network (except those tokens transmitted by this

node).

The RCVACT and TOKEN bits may help the

user to troubleshoot the network or the node. If

unusual events are occurring on the network,

the user may find it valuable to use the TXEN bit

of the Configuration Register to qualify events.

Different combinations of the RCVACT, TOKEN,

and TXEN bits, as shown indicate different

situations:

Normal Results:

RCVACT=1, TOKEN=1, TXEN=0: The node is

not part of the network. The network is

operating properly without this node.

RCVACT=1, TOKEN=1, TXEN=1: The node

sees receive activity and sees the token. The

basic transmit function is enabled. Network and

node are operating properly.

MYRECON=0, DUPID=0, RCVACT=1, TXEN=0,

TOKEN=1: Single node network.

Abnormal Results:

RCVACT=1, TOKEN=0, TXEN=X: The node

sees receive activity, but does not see the token.

Either no other nodes exist on the network,

some type of data corruption exists, the media

driver is malfunctioning, the topology is set up

incorrectly, there is noise on the network, or a

reconfiguration is occurring.

RCVACT=0, TOKEN=0, TXEN=1: No receive

activity is seen and the basic transmit function

is enabled. The transmitter and/or receiver are

not functioning properly.

RCVACT=0, TOKEN=0, TXEN=0: No receive

activity and basic transmit function disabled.

This node is not connected to the network.

The Excessive NAK (EXCNAK) bit is used to

replace a timeout function traditionally

implemented in software. This function is

necessary to limit the number of times a sender

issues a FBE to a node with no available buffer.

When the destination node replies to 128 FBEs

with 128 NAKs or 4 FBEs with 4 NAKs, the

EXCNAK bit of the sender is set, generating an

interrupt. At this point the software may

abandon the transmission via the "Disable

Transmitter" command. This sets the TA bit to

logic "1" when the node next receives the token,

to allow a different transmission to occur. The

timeout value for the EXNACK bit (128 or 4) is

determined by the FOUR-NAKS bit on the Setup

The user may choose to wait for more NAK's

before disabling the transmitter by taking

advantage of the wraparound counter of the

EXCNAK bit. When the EXCNAK bit goes high,

indicating 128 or 4 NAKs, the "POR Clear

Flags" command may be issued to reset the bit

so that it will go high again after another count

▷