COM20051I Datasheet, PDF (46/74 Pages) SMSC Corporation – Integrated Microcontroller and ARCNET (ANSI 878.1) Interface

Entering the Network
After establishing a unique Node ID, the COM20051I can join the network. Prior to actually joining the network,
several diagnostic bits should be checked to ensure that the node is properly functioning and that the network is
functioning properly. The DUPID, RCVACT, and TOKEN bits should all be checked to ensure that the network is
operating properly. A read of the Diagnostic Status register should be done to clear previous data prior to checking
the status bits. This will ensure that the Diagnostic Status bits are reflecting the latest status of the network. A period
of time lasting 840ms should elapse prior to checking the status bits. The 840ms period is a worst case situation
based on a full 255 node network with every node transmitting a 512 byte packet. The actual wait time will be less for
most systems and should be calculated based on the number of nodes and maximum packet size. Once the wait
period is over, the Diagnostic Status bits should read as follows: DUPID = 0, RCVACT = 1, and TOKEN = 1. Any
other combination indicates that a problem exists on the network. Once a valid status condition is established, the
TXEN bit of the Configuration Register should be programmed to a '1' to allow the transmitter output to drive the
network. The node is now a member of the network.
NETWORK
T
T
COM20051I
MASTE
OUT
COM20051I
SLAVE
IN OUT
COM20051I
SLAVE
IN OUT
COM20051I
SLAVE
IN OUT
0
TIME
LINE 1 LINE 2 LINE 3
LINE 1
LINE 2
LINE 3
SLAVE #3
FIGURE 15 – DAISY CHAIN METHOD OF NODE ID SELECTION
SMSC DS – COM20051I
Page 46
Rev. 03/27/2000