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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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PROTOCOL DESCRIPTION  
DATA RATES  
NETWORK PROTOCOL  
The COM20020-5 is capable of supporting data  
rates from 312.5 Kbps to 5 Mbps. The  
following protocol description assumes a 5  
Mbps data rate. For slower data rates, an  
internal clock divider scales down the clock  
frequency. Thus all timeout values are scaled  
up as shown in the following table:  
Communication on the network is based on a  
token passing protocol. Establishment of the  
network configuration and management of the  
network protocol are handled entirely by the  
COM20020-5's internal microcoded sequencer.  
A processor or intelligent peripheral transmits  
data by simply loading a data packet and its  
destination ID into the COM20020-5's  
internal  
TIMEOUT  
RAM buffer, and issuing a command to enable  
the transmitter. When the COM20020-5 next  
receives the token, it verifies that the receiving  
node is ready by first transmitting a FREE  
BUFFER ENQUIRY message. If the receiving  
node transmits an ACKnowledge message, the  
data packet is transmitted followed by a 16-bit  
CRC. If the receiving node cannot accept the  
packet (typically its receiver is inhibited), it  
transmits a Negative AcKnowledge message  
and the transmitter passes the token. Once it  
has been established that the receiving node  
can accept the packet and transmission is  
complete, the receiving node verifies the packet.  
If the packet is received successfully, the  
receiving node transmits an ACKnowledge  
message (or nothing if it is not received  
successfully) allowing the transmitter to set the  
appropriate status bits to indicate successful or  
unsuccessful delivery of the packet. An interrupt  
mask permits the COM20020-5 to generate an  
interrupt to the processor when selected status  
bits become true. Figure 1 is a flow chart  
illustrating the internal operation of the  
CLOCK  
PRESCALER  
DATA RATE  
W/20MHz XTAL  
SCALING  
FACTOR  
(MULTIPLY BY)  
÷8  
÷16  
÷32  
÷64  
÷128  
5 Mbps  
2.5 Mbps  
1.25 Kbps  
625 Kbps  
312.5 Kbps  
1
2
4
8
16  
Example: IDLE LINE Timeout @ 5 Mbps = 41  
s. IDLE LINE Timeout for 312.5 Kbps is 41  
* 16 = .66 ms  
s
m
m
NETWORK RECONFIGURATION  
A significant advantage of the COM20020-5 is  
its ability to adapt to changes on the network.  
Whenever  
deactivated,  
RECONFIGURATION is performed. When a  
new COM20020-5 is turned on (creating  
new active node on the network), or if the  
COM20020-5 has not received an INVITATION  
TO TRANSMIT for 420mS, or if a software reset  
occurs, the COM20020-5 causes a NETWORK  
a
new node is activated or  
NETWORK  
a
a
COM20020-5  
connected to a 40 MHz crystal  
oscillator.  
RECONFIGURATION  
by  
sending  
a
RECONFIGURE BURST consisting of eight  
marks and one space repeated 765 times. The  
purpose of this burst is to terminate all activity  
on the network. Since this burst is longer than  
any other type of transmission, the burst will  
interfere with the next INVITATION TO  
TRANSMIT, destroy the token and keep any  
other node from assuming control of the line.  
8