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CS8900A 参数 Datasheet PDF下载

CS8900A图片预览
型号: CS8900A
PDF下载: 下载PDF文件 查看货源
内容描述: 水晶局域网? ISA以太网控制器 [Crystal LAN ⑩ ISA Ethernet Controller]
分类和应用: 控制器局域网以太网
文件页数/大小: 128 页 / 1360 K
品牌: CIRRUS [ CIRRUS LOGIC ]
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CS8900A  
Crystal LAN™ ISA Ethernet Controller  
5.2.3.2 Early Interrupt Generation  
CTL register (Register 5). If the receive frame  
passes the Acceptance filter, the frame is buffered,  
either on chip or in host memory via DMA. If the  
frame fails the Acceptance filter, it is discarded.  
The results of the Acceptance filter are reported in  
the RxEvent register (Register 4).  
The CS8900A support the following two early in-  
terrupts that can be used to inform the host that a  
frame is being received:  
RxDest: The RxDest bit (Register C, BufEvent,  
Bit F) is set as soon as the Destination Address  
(DA) of the incoming frame passes the DA fil-  
ter. If the RxDestiE bit (Register B, BufCFG,  
bit F) is set, the CS8900A generates a corre-  
sponding interrupt. Once RxDest is set, the host  
is allowed to read the incoming frame's DA (the  
first 6 bytes of the frame).  
5.2.3.4 Normal Interrupt Generation  
The final step of pre-processing is to generate any  
enabled interrupts that are triggered by the incom-  
ing frame. Interrupt generation occurs when the en-  
tire frame has been buffered (up to the first 1518  
bytes). For more information about interrupt gener-  
ation, see Section 5.1 on page 79.  
Rx128: The Rx128 bit (Register C, BufEvent,  
Bit B) is set as soon as the first 128 bytes of the  
incoming frame have been received. If the  
Rx128iE bit (Register B, BufCFG, bit B) is set,  
the CS8900A generates a corresponding inter-  
rupt. Once the Rx128 bit is set, the RxDest bit  
is cleared and the host is allowed to read the  
first 128 bytes of the incoming frame. The  
Rx128 bit is cleared by the host reading the  
BufEvent register (either directly or through the  
Interrupt Status Queue) or by the CS8900A de-  
tecting the incoming frame's End-of-Frame  
(EOF) sequence.  
5.2.4 Held vs. DMAed Receive Frames  
All accepted frames are either held in on-chip  
RAM until processed by the host, or stored in host  
memory via DMA. A receive frame that is held in  
on-chip RAM is referred to as a held receive frame.  
A frame that is stored in host memory via DMA is  
a DMAed receive frame. This section describes  
buffering and transferring held receive frames.  
Section 5.4 on page 90 through Section 5.6 on  
page 96 describe DMAed receive frames.  
5.2.5 Buffering Held Receive Frames  
If space is available, an incoming frame will be  
temporarily stored in on-chip RAM, where it  
awaits processing by the host. Although this re-  
ceive frame now occupies on-chip memory, the  
CS8900A does not commit the memory space to it  
until one of the following two conditions is true:  
Like all Event bits, RxDest and Rx128 are set by  
the CS8900A whenever the appropriate event oc-  
curs. Unlike other Event bits, RxDest and Rx128  
may be cleared by the CS8900A without host inter-  
vention. All other event bits are cleared only by the  
host reading the appropriate event register, either  
directly or through the Interrupt Status Queue  
(ISQ). (RxDest and Rx128 can also be cleared by  
the host reading the BufEvent register, either di-  
rectly or through the Interrupt Status Queue). Fig-  
ure 22 provides a diagram of the Early Interrupt  
process.  
1) The entire frame has been received and the host  
has learned about the frame by reading the Rx-  
Event register (Register 4), either directly or  
through the ISQ.  
Or:  
2) The frame has been partially received, causing  
either the RxDest bit (Register C, BufEvent, Bit  
F) or the Rx128 bit (Register C, BufEvent, Bit  
B) to become set, and the host has learned about  
5.2.3.3 Acceptance Filtering  
The third step of pre-processing is to determine  
whether or not to accept the frame by comparing  
the frame with the criteria programmed into the Rx-  
CIRRUS LOGIC PRODUCT DATA SHEET  
84  
DS271PP3