
SiS5595 PCI System I/O Chipset
Preliminary V2.0 Nov. 2, 1998 59 Silicon Integrated Systems Corporation
R6Dh bit 0: Keyboard Hot-key Control
R70h bit 4: Enable KLOCK# Function
R70h bit3: Enable Built-in Keyboard Controller
R70h bit2: Enable PS/2 Mouse Mode
3.9
ISA BUS INTERFACE
3.9.1 ISA BUS CONTROLLER
The SiS5595’s ISA Bus Interface accepts those cycles from PCI bus interface and then
translates them onto the ISA bus. It also requests the PCI master bridge to generate PCI
cycle on behalf of DMA or ISA master devices. The ISA bus interface thus contains a
standard ISA Bus Controller (IBC) and Data Buffering logic. IBC provides all the ISA control,
such as ISA command generation, I/O recovery control, wait-state insertion, and data buffer
steering. The PCI to/from ISA address and data bus buffering are also integrated in SiS5595.
The SiS5595 can directly support 4 ISA slots without external data or address buffering.
Standard ISA bus refresh is requested by Counter 1, and then performed via the IBC. IBC
generates the pertinent command and refresh address to the ISA bus. Since the ISA refresh
is transparent to the PCI bus and the DMA cycle, an arbiter is employed to resolve the
possible conflicts among PCI cycles, refresh cycles, and DMA cycles.
3.9.2 DMA CONTROLLER
The SiS5595 contains a seven-channel DMA controller. Channels 0 to 3 are for 8-bit DMA
devices while channels 5 to 7 are for 16-bit devices. The channels can also be programmed
for any of the four transfer modes, which include single, demand, block, and cascade.
Except in cascade mode, each of the three active transfer modes can perform three different
types of transfers, which include read, write, and verify. The address generation circuitry in
SiS5595 can support 32-bit address for DMA devices.
3.9.3 INTERRUPT CONTROLLER
The SiS5595 provides an ISA compatible interrupt controller that incorporates the
functionality of two 8259 interrupt controllers. The two controllers are cascaded so that 14
external and two internal interrupts are supported. The master interrupt controller provides
IRQ<7:0> and the slave provides IRQ<15:8>. The two internal interrupts are used for internal
functions only and are not available externally. IRQ2 is used to cascade the two controllers
together and IRQ0 is used as a system timer interrupt and is tied to interval Counter 0. The
remaining 14 interrupt lines are available for external system interrupts.
Table 3.9-1 8259 IRQs Mapping
PRIORITY
1
2
3-10
3
4
LABEL
IRQ0
IRQ1
IRQ2
IRQ8#
IRQ9
CONTROLLER
1
1
1
2
2
TYPICAL INTERRUPT SOURCE
Timer/Counter 0 Out
Keyboard
Interrupt from Controller 2
Real Time Clock
Expansion bus pin B04