COM20051I Datasheet, PDF (41/74 Pages) SMSC Corporation – Integrated Microcontroller and ARCNET (ANSI 878.1) Interface

The Tentative ID Register may be used to build a network map of all the nodes on the network, even once the
COM20051I has joined the network. Once a value is placed in the Tentative ID Register, the ARCNET core 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.
IMPROVED DIAGNOSTICS
The COM20051I 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 Register
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 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 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.
SMSC DS – COM20051I
Page 41
Rev. 03/27/2000