COM20020ILJP datasheet(48/72 Pages) MICROCHIP

48 / 72 page

5Mbps ARCNET (ANSI 878.1) Controller with 2K x 8 On-Chip RAM

Datasheet

Revision 12-05-06

Page 48

SMSC COM20020I Rev D

DATASHEET

The Tentative ID Register may be used to build a network map of all the nodes on the network, even once

the COM20020ID has joined the network.

Once a value is placed in the Tentative ID Register, the

COM20020ID looks for a response to a token whose DID matches the Tentative ID Register.

The

software can record this information and continue placing Tentative ID values into the register to continue

building the network map. A complete network map is only valid until nodes are added to or deleted from

the network. Note that a node cannot detect the existence of the next logical node on the network when

using the Tentative ID. To determine the next logical node, the software should read the Next ID Register.

6.8

Improved Diagnostics

The COM20020ID allows the user to better manage the operation of the network through the use of the

internal Diagnostic Status Register.

A high level on the My Reconfiguration (MYRECON) bit indicates that the Token Reception Timer of this

node expired, causing a reconfiguration by this node. After the Reconfiguration (RECON) bit of the Status

the Diagnostic Status Register.

Reading the Diagnostic Status Register resets the MYRECON bit.

Successive 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 Register to enable the basic

transmit function. 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

indicate different situations:

6.8.1

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.

6.8.2

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.

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