PC87570-ICCSLASHVUL datasheet(60/168 Pages) NSC

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Host Bus Interface (HBI)

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3. Perform two write operations with data 00h to the same

address (as used in steps 2 and 3) to reset any other de-

vice that may have been accidentally enabled by the ad-

dress write operations. Software can now access the

configuration Index and Data Registers, for setting the

PC87570 interface according to the system configura-

tion.

Once the initial setting of the configuration registers is suc-

cessfully completed, it cannot be set again until reset is ap-

plied. Figure 5-7 illustrates the flow of the PnP protocol

described above.

Two addresses of the host bus I/O address space are used

to access the configuration registers. These addresses hold

the Configuration Index and the Configuration Data Regis-

ter pair. The address of these registers is defined by the

SBAH and SBAL Registers.

The configuration Index Register points to the configuration

from/to the Data Register, respectively.

5.13.2

Operation Guidelines

Changing Data

One write operation is required to change the contents of a

configuration register.Use one of the following procedures

for changing data in the configuration registers.

Modify Only

1. Write to the Index Register the index of the configuration

you want to modify the FER Register.

2. Write the new data for the configuration register to the

configuration Data Register.

Read, Modify, Write

1. Write to the Index Register the index of the configuration

you want to modify the FER Register.

2. Read the contents of that configuration register from the

Data Register.

3. Write the modified data for the configuration register to

the Data Register.

Reserved Bits

To maintain compatibility with future chips, the host soft-

ware should avoid modification of reserved bits whenever

the register is written. You can use a read-modify-write se-

quence to preserve the value of reserved bits.

Conﬂict Notice

When setting the addresses of different devices, ensure

that no two devices are configured to the same address.

Configuring two devices (or a device and the configuration

Index/Data registers) to the same address may have unpre-

dictable results.

Changing the Conﬁguration Base Address

This scheme allows the host to change the location of the

SBAH and SBAL Registers. This protocol may be per-

formed whenever access to the configuration registers is

enabled; i.e., after it was first set using the PnP protocol and

if SBALK in the FLR Register is 0.

The address used should meet the following criteria:

The address loaded into SBAH and SBAL should al-

ways be an even address (i.e., SBAL.0=0, data written

to it is ignored).

The address points to the conﬁguration Index Register,

and the conﬁguration Data Register is at the next con-

secutive address.

When changing the base address, the host should perform

two data write operations as described in “Changing Data”

on page 60. The data writes should be as follows:

1. Update the eight high bits of the configuration Index

This updates an internal temporary register. SBAH is

not yet updated. Reading SBAH at this point returns the

data it contained before the write.

The addresses of the Index and Data registers have not

yet changed.

2. Update the eight lower bits of the configuration Index

This write operation updates both the SBAH and SBAL

registers with the data stored in the temporary register

and the currently written data, respectively.

The addresses of the configuration Index and Data Reg-

isters are now changed.

When required, this process may be repeated.

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