82371SB datasheet(13/122 Pages) INTEL

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82371FB (PIIX) AND 82371SB (PIIX3)

1.4.

ISA Interface Signals

Signal Name

Type

Description

BALE

BUS ADDRESS LATCH ENABLE: BALE is an active high signal asserted

by the PIIX/PIIX3 to indicate that the address (SA[19:0], LA[23:17]) and

SBHE# signal lines are valid.

AEN

ADDRESS ENABLE: AEN is asserted during DMA cycles to prevent I/O

slaves from misinterpreting DMA cycles as valid I/O cycles. This signal is

also driven high during PIIX/PIIX3 initiated refresh cycles.

For the PIIX, when TC is sampled low on the assertion of PWORK (External

DMA mode), the PIIX tri-states this signal.

SYSCLK

ISA SYSTEM CLOCK: SYSCLK is the reference clock for the ISA Bus and

drives the bus directly. SYSCLK is generated by dividing PCICLK by 3 or 4.

The SYSCLK frequencies supported are 7.5 MHz and 8.33 MHz. SYSCLK

is a divided down version of PCICLK.

Hardware Strapping Option

SYSCLK is tri-stated when PWROK is negated. The value of SYSCLK is

sampled on the assertion of PWROK: If sampled high, the ISA clock divisor

is 3 (for 25 MHz PCI). If sampled low, the divisor is 4 (for 30 and 33 MHz

PCI).

IOCHRDY

I/O

I/O CHANNEL READY: Resources on the ISA Bus negate IOCHRDY to

indicate that additional time (wait states) is required to complete the cycle.

This signal is normally high on the ISA Bus. IOCHRDY is an input when the

PIIX/PIIX3 owns the ISA Bus and the CPU or a PCI agent is accessing an

ISA slave or during DMA transfers. IOCHRDY is output when an external

ISA Bus Master owns the ISA Bus and is accessing DRAM or a PIIX/PIIX3

IOCS16#

16-BIT I/O CHIP SELECT: This signal is driven by I/O devices on the ISA

Bus to indicate that they support 16-bit I/O bus cycles.

IOCHK#

I/O CHANNEL CHECK: IOCHK# can be driven by any resource on the ISA

Bus. When asserted, it indicates that a parity or an uncorrectable error has

occurred for a device or memory on the ISA Bus. If enabled, a NMI is

generated to the CPU.

IOR#

I/O

I/O READ: IOR# is the command to an ISA I/O slave device that the slave

may drive data on to the ISA data bus (SD[15:0]).

IOW#

I/O

I/O WRITE: IOW# is the command to an ISA I/O slave device that the slave

may latch data from the ISA data bus (SD[15:0]).

LA[23:17]/

CS1S

CS3S

CS1P

CS3P

DA[2:0]

I/O/

UNLATCHED ADDRESS: The LA[23:17] address lines are bi-directional.

These address lines allow accesses to physical memory on the ISA Bus up

to 16 Mbytes.

The LA[23:17] are also used to drive the IDE interface chip selects and

address lines via an external ALS244 buffer. See the IDE Interface signal

descriptions.

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