com20020-5 Standard Microsystems Corp., com20020-5 Datasheet - Page 39

• Manufacturer Part Number: com20020-5
• Description: Com20020-5 Ulanc Universal Local Area Network Controller With 2k X 8 On-board Ram
• Manufacturer: Standard Microsystems Corp.

MYRECON
Register.
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
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.
operating properly without this node.
RCVACT=1, TOKEN=1, TXEN=1:
sees receive activity and sees the token. The
basic transmit function is enabled. Network and
node are operating properly.
Reading the Diagnostic Status
bit
entire network is not held down
of
the
Diagnostic
The network is
The node
Status
39
MYRECON=0, DUPID=0, RCVACT=1, TXEN=0,
TOKEN=1: Single node network.
Abnormal Results:
RCVACT=1, TOKEN=0, TXEN=X:
sees receive activity, but does not see the token.
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:
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:
activity and basic transmit function disabled.
This node is not connected to the network.
The Excessive NAK (EXCNAK) bit is used to
replace
implemented in software.
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.
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
Register.
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
Either no other nodes exist on the network,
a
At this point the software may
timeout
function
This function is
traditionally
No receive
No receive
The node