
PC Card Controller Programming Model
84
September 2005
SCPS110
4.19 CardBus Memory Base Registers 0, 1
These registers indicate the lower address of a PCI memory address range. They are used by the controller
to determine when to forward a memory transaction to the CardBus bus, and likewise, when to forward a
CardBus cycle to PCI. Bits 3112 of these registers are read/write and allow the memory base to be located
anywhere in the 32-bit PCI memory space on 4-Kbyte boundaries. Bits 110 are read-only and always return
000h. Writes to these bits have no effect. Bits 8 and 9 of the bridge control register (PCI offset 3Eh, see Section
4.25) specify whether memory windows 0 and 1 are prefetchable or nonprefetchable. The memory base
register or the memory limit register must be nonzero in order for the controller to claim any memory
transactions through CardBus memory windows (i.e., these windows by default are not enabled to pass the
first 4 Kbytes of memory to CardBus).
PCI register offset:
1Ch, 24h
Register type:
Read-only, Read/Write
Default value:
0000 0000h
BIT NUMBER
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
RESET STATE
0
BIT NUMBER
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
RESET STATE
0
4.20 CardBus Memory Limit Registers 0, 1
These registers indicate the upper address of a PCI memory address range. They are used by the controller
to determine when to forward a memory transaction to the CardBus bus, and likewise, when to forward a
CardBus cycle to PCI. Bits 3112 of these registers are read/write and allow the memory base to be located
anywhere in the 32-bit PCI memory space on 4-Kbyte boundaries. Bits 110 are read-only and always return
000h. Writes to these bits have no effect. Bits 8 and 9 of the bridge control register (PCI offset 3Eh, see Section
4.25) specify whether memory windows 0 and 1 are prefetchable or nonprefetchable. The memory base
register or the memory limit register must be nonzero in order for the controller to claim any memory
transactions through CardBus memory windows (i.e., these windows by default are not enabled to pass the
first 4 Kbytes of memory to CardBus).
PCI register offset:
20h, 28h
Register type:
Read-only, Read/Write
Default value:
0000 0000h
BIT NUMBER
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
RESET STATE
0
BIT NUMBER
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
RESET STATE
0