COM20019I3V-DZD SMSC, COM20019I3V-DZD Datasheet - Page 13

• Manufacturer Part Number: COM20019I3V-DZD
• Description: Network Controller & Processor ICs ARCNET Contrllr
• Manufacturer: SMSC

Specifications of COM20019I3V-DZD

• Product: Controller Area Network (CAN)
• Number Of Transceivers: 1
• Data Rate: 312.5 Kbps
• Supply Voltage (max): 5.5 V
• Supply Voltage (min): 3 V
• Supply Current (max): 25 mA
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Package / Case: PLCC-28
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

4.4
4.5
4.5.1
4.5.2
SMSC COM20019I 3.3V Rev.C
Cost Competitive ARCNET (ANSI 878.1) Controller with 2K x 8 On-Chip RAM
then to all other nodes by decrementing the destination Node ID. If the timeout expires with no line
activity, the COM20019I 3V starts sending INVITATION TO TRANSMIT with the Destination ID (DID)
equal to the currently stored NID. Within a given network, only one COM20019I 3V will timeout (the one
with the highest ID number). After sending the INVITATION TO TRANSMIT, the COM20019I 3V waits for
activity on the line. If there is no activity for 597.6uS, the COM20019I 3V increments the NID value and
transmits another INVITATION TO TRANSMIT using the NID equal to the DID. If activity appears before
the 597.6 S timeout expires, the COM20019I 3V releases control of the line.
RECONFIGURATION, INVITATIONS TO TRANSMIT are sent to all NIDs (1-255).
Each COM20019I 3V on the network will finally have saved a NID value equal to the ID of the COM20019I
3V that it released control to. At this point, control is passed directly from one node to the next with no
wasted INVITATIONS TO TRANSMIT being sent to ID's not on the network, until the next NETWORK
RECONFIGURATION occurs. When a node is powered off, the previous node attempts to pass the token
to it by issuing an INVITATION TO TRANSMIT. Since this node does not respond, the previous node
times out and transmits another INVITATION TO TRANSMIT to an incremented ID and eventually a
response will be received.
The NETWORK RECONFIGURATION time depends on the number of nodes in the network, the
propagation delay between nodes, and the highest ID number on the network, but is typically within the
range of 192 to 488 mS.
BROADCAST MESSAGES
Broadcasting gives a particular node the ability to transmit a data packet to all nodes on the network
simultaneously. ID zero is reserved for this feature and no node on the network can be assigned ID zero.
To broadcast a message, the transmitting node's processor simply loads the RAM buffer with the data
packet and sets the DID equal to zero. Figure 4 illustrates the position of each byte in the packet with the
DID residing at address 0X01 or 1 Hex of the current page selected in the "Enable Transmit from Page
fnn" command. Each individual node has the ability to ignore broadcast messages by setting the most
significant bit of the "Enable Receive to Page fnn" command to a logic "0".
EXTENDED TIMEOUT FUNCTION
There are three timeouts associated with the COM20019I 3V operation. The values of these timeouts are
controlled by bits 3 and 4 of the Configuration Register and bit 5 of the Setup 1 Register.
Response Time
The Response Time determines the maximum propagation delay allowed between any two nodes, and
should be chosen to be larger than the round trip propagation delay between the two furthest nodes on
the network plus the maximum turn around time (the time it takes a particular COM20019I 3V to start
sending a message in response to a received message) which is approximately 101.6 μS. The round trip
propagation delay is a function of the transmission media and network topology. For a typical system
using RG62 coax in a baseband system, a one way cable propagation delay of 248 μS translates to a
distance of about 32 miles. The flow chart in Figure 3.1 uses a value of 597.6 μS (248 + 248 + 101.6) to
determine if any node will respond.
Idle Time
The Idle Time is associated with a NETWORK RECONFIGURATION. Figure 3.1 illustrates that during a
NETWORK RECONFIGURATION one node will continually transmit INVITATIONS TO TRANSMIT until it
encounters an active node. All other nodes on the network must distinguish between this operation and an
DATASHEET
Page 13
During NETWORK
Rev. 11-07-08