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COM20020I3V-HT 参数 Datasheet PDF下载

COM20020I3V-HT图片预览
型号: COM20020I3V-HT
PDF下载: 下载PDF文件 查看货源
内容描述: 5Mbps的ARCNET ( ANSI 878.1 )控制器2K ×8片内RAM [5Mbps ARCNET (ANSI 878.1) Controller with 2K x 8 On-Chip RAM]
分类和应用: 外围集成电路数据传输控制器局域网时钟
文件页数/大小: 65 页 / 472 K
品牌: SMSC [ SMSC CORPORATION ]
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5Mbps ARCNET (ANSI 878.1) Controller with 2K x 8 On-Chip RAM  
Idle Time  
The Idle Time is associated with a NETWORK RECONFIGURATION. Figure 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 entirely idle line. During  
NETWORK RECONFIGURATION, activity will appear on the line every 41 μS. This 41 μS is equal to the Response  
Time of 37.4 μS plus the time it takes the COM20020I to start retransmitting another message (usually another  
INVITATION TO TRANSMIT).  
Reconfiguration Time  
If any node does not receive the token within the Reconfiguration Time, the node will initiate a NETWORK  
RECONFIGURATION. The ET2 and ET1 bits of the Configuration Register allow the network to operate over longer  
distances than the 2 miles stated earlier. The logic levels on these bits control the maximum distances over which the  
COM20020I can operate by controlling the three timeout values described above. For proper network operation, all  
COM20020I's connected to the same network must have the same Response Time, Idle Time, and Reconfiguration  
Time.  
5.6 Line Protocol  
The ARCNET line protocol is considered isochronous because each byte is preceded by a start interval and ended with  
a stop interval. Unlike asynchronous protocols, there is a constant amount of time separating each data byte. On a 5  
Mbps network, each byte takes exactly 11 clock intervals of 200ns each. As a result, one byte is transmitted every 2.2  
S and the time to transmit a message can be precisely determined. The line idles in a spacing (logic "0") condition. A  
logic "0" is defined as no line activity and a logic "1" is defined as a negative pulse of 100nS duration. A transmission  
starts with an ALERT BURST consisting of 6 unit intervals of mark (logic "1"). Eight bit data characters are then sent,  
with each character preceded by 2 unit intervals of mark and one unit interval of space. Five types of transmission can  
be performed as described below:  
Invitations To Transmit  
An Invitation To Transmit is used to pass the token from one node to another and is sent by the following sequence:  
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An ALERT BURST  
An EOT (End Of Transmission: ASCII code 04H)  
Two (repeated) DID (Destination ID) characters  
ALERT  
BURST  
EOT  
DID  
DID  
Free Buffer Enquiries  
A Free Buffer Enquiry is used to ask another node if it is able to accept a packet of data. It is sent by the following  
sequence:  
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An ALERT BURST  
An ENQ (ENQuiry: ASCII code 85H)  
Two (repeated) DID (Destination ID) characters  
ALERT  
BURST  
ENQ  
DID  
DID  
Data Packets  
A Data Packet consists of the actual data being sent to another node. It is sent by the following sequence:  
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An ALERT BURST  
An SOH (Start Of Header--ASCII code 01H)  
An SID (Source ID) character  
Two (repeated) DID (Destination ID) characters  
A single COUNT character which is the 2's complement of the number of data bytes to follow if a short packet is  
sent, or 00H followed by a COUNT character if a long packet is sent.  
N data bytes where COUNT = 256-N (or 512-N for a long packet)  
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SMSC COM20020I 3.3V  
Page 13  
Revision 12-06-06  
DATASHEET