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COM20020-5 参数 Datasheet PDF下载

COM20020-5图片预览
型号: COM20020-5
PDF下载: 下载PDF文件 查看货源
内容描述: 通用局域网控制器2K ×8板载RAM [Universal Local Area Network Controller with 2K x 8 On-Board RAM]
分类和应用: 控制器局域网
文件页数/大小: 58 页 / 248 K
品牌: SMSC [ SMSC CORPORATION ]
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When any COM20020-5 senses an idle line for  
greater than 41 S, which occurs only when the  
token is lost, each COM20020-5 starts an  
internal timeout equal to 73 s times the  
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 12 to 30.5 ms.  
quantity 255 minus its own ID.  
The COM20020-  
5 starts network reconfiguration by sending an  
invitation to transmit first to itself and then to all  
other nodes by decrementing the destination  
BROADCAST MESSAGES  
If the timeout expires with no line  
activity, the COM20020-5 starts sending  
INVITATION TO TRANSMIT with the  
Destination ID (DID) equal to the currently  
stored NID. Within a given network, only one  
COM20020-5 will timeout (the one with the  
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 7 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 (see Table 5) to  
a logic "0".  
Node ID.  
highest ID number).  
After sending the  
INVITATION TO TRANSMIT, the COM20020-5  
waits for activity on the line. If there is no  
activity for 37.35 S, the COM20020-5  
increments the NID value and transmits another  
INVITATION TO TRANSMIT using the NID  
equal to the DID. If activity appears before the  
37.35 S timeout expires, the COM20020-5  
releases control of the line. During NETWORK  
RECONFIGURATION,  
INVITATIONS  
TO  
TRANSMIT are sent to all  
Node ID's (1 - 255).  
EXTENDED TIMEOUT FUNCTION  
Each COM20020-5 on the network will finally  
have saved a NID value equal to the ID of the  
COM20020-5 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  
There are three timeouts associated with the  
COM20020-5 operation. The values of these  
timeouts are controlled by bits 3 and 4 of the  
Configuration Register and  
bit 5 of the Setup  
Register.  
network,  
until  
the  
next  
NETWORK  
(ET1, ET2, ET3)  
Response Time  
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 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 COM20020-5 to start sending  
a
message in response to a received message)  
which is approximately 6.35 S. The round trip  
propagation delay is  
a
function of the  
transmission media and network topology. For  
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