10 Mbps ARCNET (ANSI 878.1) Controller with 2Kx8 On-Board RAM
Datasheet
internal registers may be written to. Since writing a non-zero value to the Node ID Register wakes up the
core, the Setup1 Register should be written to before the Node ID Register. Until a non-zero value is
placed into the NID Register, no microcode is executed, no tokens are passed by this node, and no
reconfigurations are generated by this node. Once a non-zero value is placed in the register, the core
wakes up, but the node will not attempt to join the network until the TX Enable bit of the Configuration
Register is set.
Before setting the TX Enable bit, the software may make some determinations. The software may first
observe the Receive Activity and the Token Seen bits of the Diagnostic Status Register to verify the health
of the receiver and the network.
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 210mS (or 420mS if the ET1
and ET2 bits are other than 1,1). To determine if another node on the network already has this ID, the
COM20022I 3V 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 210mS 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 COM20022I 3V has joined the network. Once a value is placed in the Tentative ID Register, the
COM20022I 3V 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.
6.6
Improved Diagnostics
The COM20022I 3V 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
Revision 02-27-06
Page 54
SMSC COM20022I 3V
DATASHEET
SMSC [ SMSC CORPORATION ]
