PCI6421 datasheet(110/204 Pages) TI

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4−34

4.47 Serial Bus Data Register

The serial bus data register is for programmable serial bus byte reads and writes. This register represents the data

when generating cycles on the serial bus interface. To write a byte, this register must be programmed with the data,

the serial bus index register must be programmed with the byte address, the serial bus slave address must be

programmed with the 7-bit slave address, and the read/write indicator bit must be reset.

On byte reads, the byte address is programmed into the serial bus index register, the serial bus slave address register

must be programmed with both the 7-bit slave address and the read/write indicator bit, and bit 5 (REQBUSY) in the

serial bus control and status register (see Section 4.50) must be polled until clear. Then the contents of this register

are valid read data from the serial bus interface. See Table 4−22 for a complete description of the register contents.

Bit

Name

Serial bus data

Type

Default

Serial bus data

Offset:

B0h (function 0)

Type:

Read/Write

Default:

00h

Table 4−22. Serial Bus Data Register Description

BIT

SIGNAL

TYPE

FUNCTION

7−0 ‡

SBDATA

Serial bus data. This bit field represents the data byte in a read or write transaction on the serial interface.

On reads, the REQBUSY bit must be polled to verify that the contents of this register are valid.

‡ One or more bits in this register are cleared only by the assertion of GRST.

4.48 Serial Bus Index Register

The serial bus index register is for programmable serial bus byte reads and writes. This register represents the byte

address when generating cycles on the serial bus interface. To write a byte, the serial bus data register must be

programmed with the data, this register must be programmed with the byte address, and the serial bus slave address

must be programmed with both the 7-bit slave address and the read/write indicator.

On byte reads, the word address is programmed into this register, the serial bus slave address must be programmed

with both the 7-bit slave address and the read/write indicator bit, and bit 5 (REQBUSY) in the serial bus control and

status register (see Section 4.50) must be polled until clear. Then the contents of the serial bus data register are valid

read data from the serial bus interface. See Table 4−23 for a complete description of the register contents.

Bit

Name

Serial bus index

Type

Default

Serial bus index

Offset:

B1h (function 0)

Type:

Read/Write

Default:

00h

Table 4−23. Serial Bus Index Register Description

BIT

SIGNAL

TYPE

FUNCTION

7−0 ‡

SBINDEX

Serial bus index. This bit field represents the byte address in a read or write transaction on the serial interface.

‡ One or more bits in this register are cleared only by the assertion of GRST.

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