COM20020 datasheet(47/72 Pages) SMSC

47 / 72 page

Next, the uniqueness of the Node ID value placed

in the Node ID Register is determined. The TX

Enable bit should still be a logic "0" until it is

ensured that the Node ID is unique. If this node

ID already exists, the Duplicate ID bit of the

Diagnostic Status Register is set after a maximum

of 420mS (or 840mS if the ET1 and ET2 bits are

other than 1,1). To determine if another node on

the network already has this ID, the COM20020

compares the value in the Node ID Register with

the DID's of the token, and determines whether

there is a response to it.

Once the Diagnostic

Status Register is read, the DUPID bit is cleared.

The user may then attempt a new ID value, wait

420mS before checking the Duplicate ID bit, and

repeat the process until a unique Node ID is

found. At this point, the TX Enable bit may be set

to allow the node to join the network. Once the

node joins the network, a reconfiguration occurs,

as usual, thus setting the MYRECON bit of the

Diagnostic Status Register.

The Tentative ID Register may be used to build a

network map of all the nodes on the network, even

once the COM20020 has joined the network.

Once a value is placed in the Tentative ID

token whose DID matches the Tentative ID

and continue placing Tentative ID values into the

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.

IMPROVED DIAGNOSTICS

The COM20020 allows the user to better manage

the operation of the network through the use of the

internal Diagnostic Status Register.

high

level

the

Reconfiguration

(MYRECON)

bit

indicates

that

the

Token

Reception Timer of this node expired, causing a

reconfiguration

this

node.

After

the

Reconfiguration

(RECON)

bit

the

Status

interrupts

the

microcontroller,

the

interrupt service routine will typically read the

MYRECON bit of 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

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.

COM20020 Datasheet(PDF) 47 Page - SMSC Corporation

COM20020 Datasheet(HTML) 47 Page - SMSC Corporation

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