SB4002A_Data Sheet_EN

SB4002A
26
For I/O Space
1
131
Reserved
Base Address
I/O Space Indicator
0
Table 2-17. Base Address Register for I/O space
Bit[31:2] : This bit sets the base address of this I/O space. It is used by the address decoder. [W/R]
Bit[1] : Reserved. [RO]
Bit[0] : This bit indicates that Base Address Register maps I/O Space. [RO]
Tips : How to set the Base Address
Bit[31:4] of the memory base address and Bit[31:2] of the I/O base address are used to indicate the size and
location of the I/O Space. BIOS and OS check the size of the I/O Space from this register, and designate the
appropriate address.
Set all the address bits of the required I/O Space to read only 0 bit, and other upper bits to read/write. For
example, in order to set the 1Kbyte memory space, set Bit[9:4] to hardwired 0h, and set the upper bits to
read/write bits. Now BIOS or OS writes FFFFFFFFh on the entire base address register, reads the hardwired
0 bits to check the size of the I/O space, and then, writes the appropriate address on the base address
register. The internal address decoder determines access to the I/O space based on this address. The base
address registers which are not used are set to all ‘1’.
* SB4002A allocates the Base Address0 or Base Address5 for access of the internal control register
(selective). The internal register is 28 bytes, and is in the I/O Space or the Memory Space (selective). The
default value of the Base Address0 register is FFFFFFC1h or FFFFFFC0h.
Bit[5:0] is a Read Only bit and Bit[31:6] is a Read/Write bit.
* How to select the I/O Space: The Base Address register and the type of the I/O Space are determined by
00h and 01h of the Serial ROM. If 00h is 0b, the base address is allocated to Base Address0, and if it is 1b,
to Base Address5. If 01h is 0b, the base address is allocated to I/O space, and if it is 1b, to the Memory
Space.