WM8281ECSSLASHR datasheet(177/392 Pages) CIRRUS

177 / 392 page

WM8281

Rev 4.0

177

are implemented using the “CHANGE_VALUE” and “REQUEST_VALUE”

messages. A maximum of two messages may be required, depending on circumstances: the

“CHANGE_VALUE” message selects the register page (bits [23:8] of the Control Register address);

the “REQUEST_VALUE” message contains bits [7:0] of the register address. The first message may

be omitted if the register page is unchanged from the previous Read or Write operation.

The associated parameters are described in Table 56 and Table 57, for the generic case of reading

the contents of control register address 0xYYYYZZ.

Read Message 1

– CHANGE_VALUE

PARAMETER

VALUE

DESCRIPTION

Source Address

0xSS

‘SS’ is the 8-bit Logical Address of the message

source. This could be any active device on the bus,

but is typically the Manager Device (0xFF).

Destination Address

0xLL

‘LL’ is the 8-bit Logical Address of the message

destination (ie. the WM8281 SLIMbus Interface

Device). The value is assigned by the SLIMbus

Manager Device.

Access Mode

0b1

Selects Byte-based access mode.

Byte Address

0x800

Identifies the User Value element for selecting the

Control Register page address.

Slice Size

0b001

Selects 2-byte slice size

Value Update

0xYYYY

‘YYYY’ is bits [23:8] of the applicable Control

Table 56 Register Read Message (1)

Read Message 2

– REQUEST_VALUE

PARAMETER

VALUE

DESCRIPTION

Source Address

0xSS

‘SS’ is the 8-bit Logical Address of the message

source. This could be any active device on the bus,

but is typically the Manager Device (0xFF).

Destination Address

0xLL

‘LL’ is the 8-bit Logical Address of the message

destination (ie. the WM8281 SLIMbus Interface

Device). The value is assigned by the SLIMbus

Manager Device.

Access Mode

0b1

Selects Byte-based access mode.

Byte Address

0xUUU

Specifies the Value Map address, calculated as

0xA00 + (2 x 0xZZ), where ‘ZZ’ is bits [7:0] of the

applicable Control Register address.

Slice Size

0b001

Selects 2-byte slice size

Transaction ID

0xTTTT

‘TTTT’ is the 16-bit Transaction ID for the

message. The value is assigned by the SLIMbus

Manager Device.

Table 57 Register Read Message (2)

Note that the first message may be omitted if its contents are unchanged from the previous

CHANGE_VALUE message sent to the WM8281.

The WM8281 will respond to the Register Read commands in accordance with the normal SLIMbus

protocols.

Note that the WM8281 assumes that sufficient Control Space Slots are available in which to provide

its response before the next REQUEST_VALUE message is received. The WM8281 response is

made using a REPLY_VALUE message; the SLIMbus Manager should wait until the REPLY_VALUE

message has been received before sending the next REQUEST_VALUE message. If additional

REQUEST_VALUE message(s) are received before the WM8281 response has been made, then the

earlier REQUEST_VALUE message(s) will be ignored (ie. only the last REQUEST_VALUE message

will be serviced).

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