206 AMD Geode™ SC2200 Processor Data Book
Core Logic Module - Bridge, GPIO, and LPC Registers - Function 0
32580B
Index 5Ah Decode Control Register 1 (R/W) Reset Value: 01h
Indicates PCI positive or negative decoding for various I/O ports on the ISA bus.
Note: Positive decoding by the Core Logic module speeds up I/O cycle time. The I/O ports mentioned in the bit descriptions below, do
not exist in the Core Logic module. It is assumed that if positive decode is enabled for a port, the port exists on the ISA bus.
7Secondary Floppy Positive Decode. Selects PCI positive or subtractive decoding for accesses to I/O ports 372h-375h
and 377h.
0: Subtractive.
1: Positive.
6Primary Floppy Positive Decode. Selects PCI positive or subtractive decoding for accesses to I/O ports 3F2h-3F5h and
3F7h.
0: Subtractive.
1: Positive.
5COM4 Positive Decode. Selects PCI positive or subtractive decoding for accesses to I/O ports 2E8h-2EFh.
0: Subtractive.
1: Positive.
4COM3 Positive Decode. Selects PCI positive or subtractive decoding for accesses to I/O ports 3E8h-3EFh.
0: Subtractive.
1: Positive.
3COM2 Positive Decode. Selects PCI positive or subtractive decoding for accesses to I/O ports 2F8h-2FFh.
0: Subtractive.
1: Positive.
2COM1 Positive Decode. Selects PCI positive or subtractive decoding for accesses to I/O ports 3F8h-3FFh.
0: Subtractive.
1: Positive.
1Keyboard Controller Positive Decode. Selects PCI positive or subtractive decoding for accesses to I/O Ports 060h and
064h (as well as 062h and 066h, if enabled - F4 Index 5Bh[7] = 1).
0: Subtractive.
1: Positive.
Note: If F0BAR1+I/O Offset 10h bits 10 = 0 and 16 = 1, then this bit must be written 0.
0Real-Time Clock Positive Decode. Selects PCI positive or subtractive decoding for accesses to I/O Ports 070h-073h.
0: Subtractive.
1: Positive.
Index 5Bh Decode Control Register 2 (R/W) Reset Value: 20h
Note: Positive decoding by the Core Logic module speeds up the I/O cycle time. The Keyboard, LPT3, LPT2, and LPT1 I/O ports do
not exist in the Core Logic module. It is assumed that if positive decoding is enabled for any of these ports, the port exists on
the ISA bus.
7Keyboard I/O Port 062h/066h Positive Decode. This alternate port to the keyboard controller is provided in support of
power management features.
0: Disable.
1: Enable.
6Reserved. Must be set to 0.
5BIOS ROM Positive Decode. Selects PCI positive or subtractive decoding for accesses to the configured ROM space.
0: Subtractive.
1: Positive.
ROM configuration is at F0 Index 52h[2:0].
4Secondary IDE Controller Positive Decode. Selects PCI positive or subtractive decoding for accesses to I/O ports 170h-
177h and 376h-377h (excluding writes to 377h).
0: Subtractive. Subtractively decoded IDE addresses are forwarded to the PCI slot bus. If a master abort occurs, they are
then forwarded to ISA.
1: Positive. Positively decoded IDE addresses are forwarded to the internal IDE controller and then to the IDE bus.
Table 6-29. F0: PCI Header/Bridge Configuration Registers for GPIO and LPC Support (Continued)
Bit Description