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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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byte.  
Each byte takes exactly 11 clock intervals  
a
typical system using RG62 coax in  
a
n
baseband system, a one way cable propagation  
that are defined by nPULSE1 and PULSE2  
t
signals (at 5 Mbps one byte is ransmitted every  
The line idles in a spacing (logic "0")  
delay of 15.5 S translates to a distance of about  
2 miles. The flow chart in Figure 1 uses a value  
m
2.2 S).  
m
condition. A logic "0" is defined as no line  
activity and a logic "1" is defined as a negative  
of 37.35 S (15.5 + 15.5 + 6.35) to determine if  
m
any node will respond.  
pulse of 100nS duration  
A
(at 5 Mbps).  
(ET1, ET2, ET3)  
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:  
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.  
(ITT)  
Invitations To Transmit  
During  
NETWORK  
RECONFIGURATION,  
An Invitation To Transmit is used to pass the  
token from one node to another and is sent by  
the following sequence:  
activity will appear on the line every 41 S. This  
m
41 S is equal to the Response Time of 37.35 S  
m
m
plus the time it takes the COM20020-5 to start  
retransmitting another message (usually another  
INVITATION TO TRANSMIT).  
An ALERT BURST  
·
An EOT (End Of Transmission: ASCII code  
04H)  
·
(ET1, ET2)  
Reconfiguration Time  
Two (repeated) DID (Destination  
ID) characters  
·
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 COM20020-5 can operate by  
controlling the three timeout values described  
ALERT  
BURST  
EOT  
DID  
DID  
(FBE)  
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:  
above.  
For proper network operation, all  
COM20020-5's connected to the same network  
must have the same Response Time, Idle Time,  
and Reconfiguration Time.  
An ALERT BURST  
·
·
·
An ENQ (ENQuiry: ASCII code 85H)  
Two (repeated) DID (Destination ID)  
characters  
LINE PROTOCOL  
The ARCNET line protocol is considered  
isochronous because each byte is preceded by a  
start interval and ended with a stop interval.  
ALERT  
BURST  
ENQ  
DID  
DID  
Unlike asynchronous protocols, there is  
a
constant amount of time separating each data  
10