COM20051I Datasheet, PDF (45/74 Pages) SMSC Corporation – Integrated Microcontroller and ARCNET (ANSI 878.1) Interface

COM20051I
A15-
D7-
ADDRES
DECODE
NID
EN
'LS24
DIP
SWITC
FIGURE 14 – NODE ID SELECTION USING A HARDWARE SWITCH READ
Method 2 - Non-Volatile Memory Storage
This method involves the storage of the Node ID in either a PROM, EPROM, or EEPROM. The microcontroller
simply reads the proper location and programs the ID value. This method is well suited for closed networks that are
not expected to expand or are maintained solely by the OEM. Such examples might include machine control and
automobiles.
Method 3 - Hardwire Daisy Chain
The Daisy Chain method uses an additional wire running from node to node in a daisy chained fashion. This type of
setup relies on a master node that uses a fixed ID value that is stored in the master node's non-volatile memory or by
reading a switch. Once the master programs its ID value it brings the additional line low. The next node that is in line
physically detects the low level on the line and uses a duplicate ID search algorithm to detect the first available ID on
the network. Once this node finds an ID and joins the network, it brings its ID line low to allow the next node to join.
This process continues until all nodes have joined the network. Figure 16 shows an example of how this is
accomplished.
Method 4 - Duplicate ID Software Search
The Duplicate ID software search is a software only method of locating available node ID values on a given network.
The basic algorithm involves a sequential search of ID values and checking their availability by using a combination
of diagnostic bits located within the ARCNET core of the COM20051I. This method is not well suited for the initial
power-up sequence of a network since there are instances in which the algorithm will assign the same ID to two
nodes when they power-up simultaneously. This occurs due to basic constraints imposed by the ARCNET protocol
itself. The Duplicate ID algorthim is very useful for adding nodes to already existing networks that use a mix of node
ID selection methods. Please refer to the section on Duplicate ID Detection for details regarding the algorithm.
SMSC DS – COM20051I
Page 45
Rev. 03/27/2000