PC87570 datasheet(53/168 Pages) NSC

53 / 168 page

Host Bus Interface (HBI)

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5.10.1

IRQ1, IRQ12 and IRQ11 and IRQ8 Buffers

The PC87570 drives the IRQ pins (IRQ1, IRQ12 and

IRQ11) using either open drain or push-pull buffers. The

buffer type is configured by PSPE in the HIIRQC Register.

When used as open drain, an external pull-up resistor is re-

quired to pull the signal high.

When the IRQE Register is set to disable IRQ1, IRQ12,

IRQ11, or IRQ8, its respective pin is put into TRI-STATE,

overriding any other settings in the host interface.

Figure 5-4 illustrates the effect of the different control bits on

the IRQ signals.

5.11 SYSTEM CONSIDERATIONS

5.11.1

Reset Configuration

During reset, the host configuration channel is initialized to

its default state, as follows:

The modules’ address registers are initialized to the

device legacy address.

The Function Enable Register is initialized according

to the HDEN strap input.

Access to the chip base address conﬁguration Index

and Data Registers is disabled.

A motherboard PnP escape sequence is enabled.

Conﬁguration lock bits are cleared.

5.11.2

Host Power-On (HPWRON) Indication Input

The PC87570 can operate when the host power is discon-

nected. In this case, the signals from the host may present

undefined states to the PC87570. A special input pin, HP-

WRON, enables the PC87570 to check the host power sup-

ply state and prevent errors caused when the supply is not

active.

When HPWRON is low, all the host interface inputs are ig-

nored and all outputs are either TRI-STATE or forced low,

according to their reset values. See “Basic Configuration”

on page 3.

When HPWRON is high, the PC87570 responds to host bus

cycles and outputs signals to it.

5.11.3

Host Master Reset (HMR) Input

The PC87570 is reset by an internal reset signal generated

on the rising edge of its power supply. The chip is also reset

on the rising edge of the HMR pin. See more details in Sec-

tion 2.3.4.

5.11.4

Host Reset Output (HRSTO) from PC87570

HRSTO is one of the sources for host soft reset commands

(i.e., INIT input in the x86 processors). See Figure 5-5. The

host is reset when the HRSTO output is low. A reset com-

mand is issued by the PC87570 when:

Hardware: Strap input HRMS=1, shared memory is

enabled (SHBM=0) and accessed while the PC87570

cannot complete the memory access. In this case, the

reset lasts until the PC87570 completes shared mem-

ory access, and HMEMRD and HMEMWR are inac-

tive. After power-up reset, the HRSTO is inactive

(high). HRSTO is automatically active (low) while HP-

WRON is low.

Software: The CR16A ﬁrmware can issue a reset com-

mand to the host by writing 1 to HRSTO in the CST2

this bit.

Hardware

HIIRQ.IRQM

Interrupt

HIIRQC.IRQNPOL

HIIRQC.IRQxB

HICTRL.OBFMIE or

HICTRL.OBFKIE

HICTRL.PMHIE or

HIIRQC.PSPE

IRQE.IRQxE

HIIRQC.IRQxB

(write)

IRQx

Figure 5-4. IRQ1, IRQ12 or IRQ11 Control

(read)

PC87570 Datasheet(PDF) 53 Page - National Semiconductor (TI)

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