AMD Geode SC2200 - Manual (Page 151)

AMD Geode™ SC2200 Processor Data Book 159
Core Logic Module 32580B
6.2.5.6 ROM Interface
The Core Logic module positively decodes memory
addresses 000F0000h-000FFFFFh (64 KB) and
FFFC0000h-FFFFFFFFh (256 KB) at reset. These memory
cycles cause the Core Logic module to claim the cycle, and
generate an ISA bus memory cycle with ROMCS#
asserted. The Core Logic module can also be configured to
respond to memory addresses FF000000h-FFFFFFFFh
(16 MB) and 000E0000h-000FFFFFh (128 KB).
8- or 16-bit wide ROM is supported. BOOT16 strap deter-
mines the width after reset. MCR[14,3] (Offset 34h) in the
General Configuration Block (see Table 4-2 on page 76 for
bit details) allows program control of the width.
Flash ROM is supported in the Core Logic module by
enabling the ROMCS# signal on write accesses to the
ROM region. Normally only read cycles are passed to the
ISA bus, and the ROMCS# signal is suppressed for write
cycles. When the ROM Write Enable bit (F0 Index 52h[1])
is set, a write access to the ROM address region causes a
write cycle to occur with MEMW#, WR# and ROMCS#
asserted.
6.2.5.7 PCI and Sub-ISA Signal Cycle Multiplexing
The SC2200 multiplexes most PCI and Sub-ISA signals on
the balls listed in Table 6-3, in order to reduce the number
of balls on the device. Cycle multiplexing is on a bus-cycle
by bus-cycle basis (see Figure 6-6 on page 160), where the
internal Core Logic PCI bridge arbitrates between PCI
cycles and Sub-ISA cycles. Other PCI and Sub-ISA signals
remain non-shared, however, some Sub-ISA signals may
be muxed with GPIO.
Sub-ISA cycles are only generated as a result of GX1 mod-
ule accesses to the following addresses or conditions:
• ROMCS# address range.
• DOCCS# address range.
• IOCS0# address range.
• IOCS1# address range.
• An I/O write to address 80h or to 84h.
• Internal ISA is programmed to be the subtractive decode
agent and no other agents claim the cycle.
If the Sub-ISA and PCI bus have more than four compo-
nents, the Sub-ISA components can be buffered using
74HCT245 or 74FCT245 type transceivers. The RD# (an
AND of IOR#, MEMR#) signal can be used as DIR control
while TRDE# is used as enable control.
Table 6-3. Cycle Multiplexed PCI / Sub-ISA Balls
PCI Sub-ISA Ball No.
AD0 A0 U1
AD1 A1 P3
AD2 A2 U3
AD3 A3 N1
AD4 A4 P1
AD5 A5 N3
AD6 A6 N2
AD7 A7 M2
AD8 A8 M4
AD9 A9 L2
AD10 A10 L3
AD11 A11 K1
AD12 A12 L4
AD13 A13 J1
AD14 A14 K4
AD15 A15 J3
AD16 A16 E1
AD17 A17 F4
AD18 A18 E3
AD19 A19 E2
AD20 A20 D3
AD21 A21 D1
AD22 A22 D2
AD23 A23 B6
AD24 D0 C2
AD25 D1 C4
AD26 D2 C1
AD27 D3 D4
AD28 D4 B4
AD29 D5 B3
AD30 D6 A3
AD31 D7 D5
C/BE0# D8 L1
C/BE1# D9 J2
C/BE2# D10 F3
C/BE3# D11 H4
PAR D12 J4
TRDY# D13 F1
IRDY# D14 F2
STOP# D15 G1
DEVSEL# BHE# E4