A-B 1756-A17/B  模块

A-B 1756-A17/B  全新 模块

A-B 1756-A17/B  全新 模块

 数据以固定大小的块在内存和缓存之间传输，称为缓存线或者缓存块。当将高速缓存行从存储器复制到高速缓存中时，创建高速缓存条目。高速缓存条目将包括复制的数据以及请求的存储器位置(称为标签)。当处理器需要读取或写入内存中的某个位置时，它首先在缓存中检查相应的条目。高速缓存在可能包含该地址的任何高速缓存行中检查所请求的存储器位置的内容。如果处理器发现内存位置在缓存中，则缓存命中已经发生了。但是，如果处理器在缓存中找不到内存位置，则会引发缓存未命中已经发生了。在高速缓存命中的情况下，处理器立即读取或写入高速缓存行中的数据。对于高速缓存未命中，高速缓存分配一个新的条目并从主存储器复制数据，然后从高速缓存的内容满足请求。

有时这被称为四相PSK，4-PSK，或4-（同QuadratureAmplitudeModulation）正交幅度调制。(虽然QPSK和4-QAM的根本概念不同，但产生的调制无线电波完全相同。)QPSK在星座图上用了四个点，围绕一个圆等距分布。通过四个相位，QPSK可以对每个符号进行两位编码，如图所示格雷编码为了最小化比特误码率(BER)——有时被误认为是BPSK的两倍。

数学分析表明，与BPSK系统相比，QPSK可用于使数据速率加倍，同时保持相同的 带宽的信号，或者保持BPSK的数据速率但是将所需带宽减半。在后一种情况下，QPSK的误码率为完全一样作为BPSK的BER当考虑或描述QPSK时，持有不同的观点是一种常见的困惑。传输的载波可以经历多次相位变化。

假设无线电通信信道是由诸如联邦通信委员会给定规定的(最大)带宽，QPSK相对于BPSK的优势变得明显:在相同的误码率下，QPSK在给定的带宽内传输的数据速率是BPSK的两倍。付出的工程代价是QPSK的****机和接收机比BPSK的更复杂。然而，随着现代电子学技术，在成本上的惩罚是非常温和的。

与BPSK一样，在接收端存在相位模糊问题差分编码实践中经常使用QPSK。

A-B 1756-A17/B  全新 模块

Data is transferred between memory and cache in fixed-size blocks, which are called cache lines or cache blocks. A cache entry is created when a cache line is copied from memory into the cache. The cache entry will include the copied data and the requested memory location (called the tag). When a processor needs to read or write to a location in memory, it first checks the corresponding entry in the cache. The cache checks the contents of the requested memory location in any cache line that may contain the address. If the processor finds that the memory location is in the cache, a cache hit has occurred. However, if the processor cannot find a memory location in the cache, it will cause a cache miss to have occurred. In case of a cache hit, the processor immediately reads or writes the data in the cache line. For cache misses, the cache allocates a new entry and copies data from the main memory, and then satisfies the request from the contents of the cache.

Sometimes this is called four-phase PSK, 4-PSK, or 4- QuadratureAmplitudeModulation. (Although the fundamental concepts of QPSK and 4-QAM are different, the modulated radio waves generated are exactly the same. QPSK uses four points on the constellation diagram, which are equally distributed around a circle. Through four phases, QPSK can encode each symbol with two bits. As shown in the figure, Gray coding is to minimize the bit error rate (BER)-sometimes mistaken for twice that of BPSK.

Mathematical analysis shows that compared with BPSK system, QPSK can be used to double the data rate while maintaining the same bandwidth, or to keep the data rate of BPSK but halve the required bandwidth. In the latter case, the bit error rate of QPSK is exactly the same. As the BER of BPSK, it is a common confusion to hold different views when considering or describing QPSK. The transmitted carrier can undergo multiple phase changes.

Assuming that the radio communication channel is the (maximum) bandwidth specified by the Federal Communications Commission, the advantages of QPSK over BPSK become obvious: at the same bit error rate, the data rate transmitted by QPSK in a given bandwidth is twice that of BPSK. The engineering cost is that the QPSK * * * machine and receiver are more complicated than BPSK. However, with the development of modern electronic technology, the cost penalty is very mild.

Like BPSK, QPSK is often used in differential coding practice with phase ambiguity at the receiving end.

A-B 1756-A17/B  全新 模块