
3.0 Device Architecture and Configuration
(Continued)
Revision 1.2
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3.2.2
Each functional block is associated with a Logical Device Number (LDN). The configuration registers are grouped into banks,
where each bank holds the standard configuration registers of the corresponding logical device. Table 9 shows the LDN val-
ues of the PC8741x functional blocks. Any value not listed is reserved.
Figure 3 shows the structure of the standard configuration register file. The LDN and ServerI/O Configuration registers are
not banked and are accessed by the Index-Data register pair only, as described above. However, the device control and
device configuration registers are duplicated over 10 banks for the 10 logical devices. Therefore, accessing a specific reg-
ister in a specific bank is performed by two-dimensional indexing, where the LDN register selects the bank (or logical device)
and the Index register selects the register within the bank. Accessing the Data register while the Index register holds a value
of 30h or higher actually accesses the configuration registers of the logical device selected by the LDN register and pointed
to by the Index register.
Banked Logical Device Registers Structure
Figure 3. Structure of Standard Configuration Register File
Table 9. Logical Device Number (LDN) Assignments
Write accesses to unimplemented registers (i.e., accessing the Data register while the Index register points to a non-existing
register) are ignored. Read accesses return 00h on all addresses, except for 74h and 75h (DMA configuration registers),
which returns 04h (indicating no DMA channel). The configuration registers are accessible immediately after reset.
LDN
Functional Block
00h
Floppy Disk Controller (FDC)
01h
Parallel Port (PP)
02h
Serial Port 2 (SP2)
03h
Serial Port 1 (SP1)
04h
System Wake-Up Control (SWC)
05h
Keyboard and Mouse Controller (KBC) - Mouse Interface
06h
Keyboard and Mouse Controller (KBC) - Keyboard Interface
07h
General-Purpose I/O (GPIO) Ports
0Fh
X-Bus Extension (
PC87416 and PC87417
)
10h
Real Time Clock (RTC)
07h
20h
2Fh
30h
60h
63h
70h
71h
75h
FEh
Logical Device Number Register
ServerI/O Configuration Registers
Logical Device Control Register
Standard Logical Device
Configuration Registers
Special (Vendor-defined)
Logical Device
Configuration Registers
Banks
F0h
Bank Select
74h
(One per Logical Device)