COM20020I3V-HT SMSC, COM20020I3V-HT Datasheet - Page 38

• Manufacturer Part Number: COM20020I3V-HT
• Description: Network Controller & Processor ICs ARCNET Contrllr
• Manufacturer: SMSC

Specifications of COM20020I3V-HT

• Product: Controller Area Network (CAN)
• Number Of Transceivers: 1
• Data Rate: 5 Mbps
• Supply Voltage (max): 3.465 V
• Supply Voltage (min): 3.135 V
• Supply Current (max): 35 mA
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Package / Case: TQFP-48
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The SID in Address 0 is used by the receiving node to reply to the transmitting node. The COM20020I 3V puts the
local ID in this location, therefore it is not necessary to write into this location. Please note that a short packet may
contain between 1 and 253 data bytes, while a long packet may contain between 257 and 508 data bytes. A
minimum value of 257 exists on a long packet so that the COUNT is expressible in eight bits. This leaves three
exception packet lengths which do not fit into either a short or long packet; packet lengths of 254, 255, or 256 bytes.
If packets of these lengths must be sent, the user must add dummy bytes to the packet in order to make the
packet fit into a long packet.
Once the packet is written into the buffer, the microcontroller awaits a logic "1" on the TA bit, indicating that a previous
transmit command has concluded and another may be issued. Each time the message is loaded and a transmit
command issued, it will take a variable amount of time before the message is transmitted, depending on the traffic on the
network and the location of the token at the time the transmit command was issued. The conclusion of the Transmit
Command will generate an interrupt if the Interrupt Mask allows it. If the device is configured for the Command Chaining
operation, please see the Command Chaining section for further detail on the transmit sequence. Once the TA bit
becomes a logic "1", the microcontroller may issue the "Enable Transmit from Page fnn" command, which resets the TA
and TMA bits to logic "0". If the message is not a BROADCAST, the COM20020I 3V automatically sends a FREE
BUFFER ENQUIRY to the destination node in order to send the message. At this point, one of four possibilities may
SMSC COM20020I 3.3V Rev.E
5Mbps ARCNET (ANSI 878.1) Controller with 2K x 8 On-Chip RAM
ADDRESS
COUNT
255
511
0
1
2
N = DATA PACKET LENGTH
SID = SOURCE ID
DID = DESTINATION ID
(DID = 0 FOR BROADCASTS)
SHORT PACKET
COUNT = 256-N
DATA BYTE N-1
DATA BYTE N
DATA BYTE 1
DATA BYTE 2
NOT USED
NOT USED
Figure 9 – Ram Buffer Packet Configuration
FORMAT
SID
DID
DATASHEET
Page 38
ADDRESS
COUNT
511
0
1
2
3
COUNT = 512-N
DATA BYTE N-1
LONG PACKET
DATA BYTE N
DATA BYTE 1
DATA BYTE 2
NOT USED
FORMAT
SID
DID
0
Revision 09-11-06