PC87570-ICCSLASHVUL datasheet(54/168 Pages) NSC

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Host Bus Interface (HBI)

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5.11.5

HDEN Strap

The HDEN strap input pin defines if the legacy devices with-

in the PC87570 are accessible from the host after reset, or

if the host must enable access to them. This impacts the

KBC, the PM, and the RTC/APC. Access to the shared

memory is not affected by this strap.

HDEN is sampled on power-up reset (see Section 2.4), but it

sets the host configuration default value on any reset.

When HDEN is low (0), the HBI is disabled and must be en-

abled using the motherboard PnP protocol.

When HDEN is high (1), the HBI is enabled with its default

legacy addresses.

5.11.6

GA20 Pin Functionality

The GA20 (Gate Address A20) is intended to implement the

memory management in a PC architecture. This allows the

access to the extended memory needed by the operating

system. In PC87570, the GA20 function is implemented by

a port used as an output. Port PB5 is recommended to be

used as GA20 since its default state after reset is output

driving high. The firmware running on the CR16A may

change the GA20 pin state by modifying the PBDOUT reg-

ister, bit 5. There is no special hardware or multiplexing on

this pin. Since there is no multiplexing, the PBALT bit 5, is

always 0, and any writes to it are disregarded. The pin may

be used as a GPIO. However, please note that this pin

wakes up differently than the other seven pins in the same

port, which are waking up as inputs.

5.11.7

Host Driven Wake-Up

When the PC87570 is in Idle mode, it will wake-up to Active

mode in response to an access on the host interface bus. A

wake-up event is sent to the MIWU (WUI26) in any of the

following cases:

Either HMEMWR or HMEMRD is active, together with

HMEMCS

Either HIORD or HIOWR is active, and the host ac-

cesses an enabled device at its valid address (i.e., ei-

ther KBC, PM, RTC, APC or the host conﬁguration

registers).

5.11.8

APC-ON and APC-OFF Events

The APC sends APC-ON to indicate a wake-up request,

and APC-OFF to indicate an off command from the host.

The APC-OFF event is enabled using APCOFFE in the

CST2 Register. To disable APC-OFF, clear this bit (and not

the MIWU Enable bit).

5.12 HBI REGISTERS ACCESSED BY CR16A

The PC87570 has 15 CR16A-accessed registers that con-

trol the host interface channel, listed with their addresses in

Table 5-2.

Table 5-2. HBI Registers Accessed by CR16A

HRSTO

Host Reset

Extend Logic

Figure 5-5. HRSTO Generation Scheme

CST2.HRSTO

SHBM=0 & HRMS=1

HMEMRD or HMEMWR are

active while MEMCS is active

Access cannot be completed

Mnemonic

Address

CST1

Control and Status Register 1

F900h

CST2

Control and Status Register 2

F902h

RTCCA

RTC Core Address Register

F904h

RTCCD

RTC Core Data Register

F906h

HCFGBAL Host Conﬁguration Base Address

Low

F908h

HCFGBAH Host Conﬁguration Base Address

High

F90Ah

HICTRL

Host Interface Control Register

FEA0h

HIIRQC

Host Interface IRQ Control Register FEA2h

HIKMST

Host Interface KBC Status Register FEA4h

HIKDO

Host Interface Keyboard Data Out

Buffer Register

FEA6h

HIMDO

Host Interface Mouse Data Out

Buffer Register

FEA8h

HIKMDI

Host Interface KBC Data In Buffer

FEAAh

HIPMST

Host Interface PM Port Status

FEACh

HIPMDO

Host Interface PM Data Out Buffer

FEAEh

HIPMDI

Host Interface PM Data In Buffer

FEB0h

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