5Mbps ARCNET (ANSI 878.1) Controller with 2K x 8 On-Chip RAM
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
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:
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.
Revision 12-05-06
Page 48
SMSC COM20020I Rev D
DATASHEET
SMSC [ SMSC CORPORATION ]
