help: 关于PCI BUS 操作寄存器MCSR中的nvRAM Access Ctrl

请各位大侠帮忙，关于PCI BUS 操作寄存器MCSR中的D[31：29]nvRAM Access Ctrl的描述，我看不懂，希望各位能指点一下。现将原文抄录如下：

31：29   nvRAM Access Control. This fieldprovides a method  for  access to the optional external non-volatile memeory.Write operations are achieved by a sequence of byte operations involving these bits and the 8-bit field of bits 23 through 16. The sequence requires that the low-order address,high order address, and then a data byte are loaded in order. Bit 31 or this field acts as a combined enable and ready for the access to the external memory. D31 must be written to a 1 before an access can begin, and sebsequent accesses must wait for bit D31 to become zero(ready).
     D31  D30  D29  W/R
      0    x    x    W     inactive
      1    0    0    W     Load low address byte
      1    0    1    W     Load high address byte
      1    1    0    W     Begin write
      1    1    1    W     begin read
      0    x    x    R     Ready
      1    x    x    R     Busy

好象不是PCI BUS的东东,应该是某个芯片或卡的西西.

   对不起，忘了说一下，这是S5933产品数据中关于PCI BUS的MCSR的nvRAM Access Ctrl描述。

不是写得很清楚了嘛。
写操作：5步
写0xx+xxxxx
写100+xxxxx+8 bit low address
写101+xxxxx+8 bit high address
写110+xxxxx+8 bit data
写0xx+xxxxx
读操作：6步
写0xx+xxxxx
写100+xxxxx+8 bit low address
写101+xxxxx+8 bit high address
写111+xxxxx
写0xx+xxxxx
读得到xxxxxx+8bit data