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PM8621 参数 Datasheet PDF下载

PM8621图片预览
型号: PM8621
PDF下载: 下载PDF文件 查看货源
内容描述: NSE- 8G⑩标准产品数据表初步 [NSE-8G⑩ Standard Product Data Sheet Preliminary]
分类和应用:
文件页数/大小: 184 页 / 957 K
品牌: PMC [ PMC-SIERRA, INC ]
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NSE-8G™ Standard Product Data Sheet  
Preliminary  
12.1.4 PCB Design Notes  
To maintain flexibility, all unused LVDS inputs and outputs should be left floating. This will  
prevent accidental damage caused by firmware enabling outputs, or releasing resets of inactive  
ports.  
12.2 “C1” Synchronization  
Any NSE/SBS fabric can be viewed as a collection of five “columns” of devices: column 0  
consists of the ingress flow from the load devices (e.g., some SBI device); column 1 consists of  
the ingress flow through the SBS devices; column 2 consists of the NSE-8G device; column 3  
consists of the egress flow through the SBS devices; and column 4 consists of the egress flow  
through the load devices (e.g. some SBI device). Note that the devices in columns 0 and 4 are  
SBI bus devices while columns 1 and 3 are SBS or SBS-lite devices. The dual column references  
refer to their two separate simplex flows. Path-aligned STS-12 frames are pipelined through this  
structure in a regular fashion, under control of a single clock source and frame pulse. There are  
latencies between these columns, and these latencies may vary from path to path. The following  
design is used to accommodate these latencies.  
A timing pulse for SBI frames (2kHz, 500=µs) is generated and fed to each device in the fabric.  
Each chip has a FrameDelay register (RC1DLY) which contains the count of 77.76 MHz clock  
ticks that device should delay from the reference timing pulse before expecting the C1 characters  
of the ingress STS-12 frames to have arrived. The base timing pulse is called t The delays from t  
.
based on the settings of the RC1DLY registers in the successive columns of the devices are called  
t , … t . The first signal, t (equal to t ), determines the start of an STS-12 frame; this signal is  
0
4
1
0
used to instruct the ingress load devices (column 0) to start emitting an STS-12 frame (with its  
special “C1” control character) at that time. t is determined by the customer, based on device and  
i
wiring delays to be approximately the earliest time that all “C1” characters will have arrived in  
the ingress FIFOs of the t column of devices. t is selected to provide assurance that all “C1”  
i
i
characters have arrived at the ith column. The ith column of devices use the t signal to synchronize  
i
emission of the STS-12 frames. The ingress FIFOs permit a variable latency in C1 arrival of up to  
16 clock cycles.  
Note: The SBS device, being a memory switch adds a latency of one complete frame or row plus  
a few clock ticks to the data.  
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use  
Document ID: PMC-2010850, Issue 1  
136