W254B Datasheet, PDF (9/16 Pages) SpectraLinear Inc – 133MHz Spread Spectrum FTG for Mobile Pentium® III Platforms

W254B
1 bit
7 bits
1
Start bit Slave Address
R/W
1
8 bits
1
Ack
Command Code
Ack
Byte Count = N
Ack Data Byte 1
Ack
1 bit
8 bits
1
Data Byte 2 Ack
8 bits
1
...
Data Byte N
Ack
Stop
8 bits
1
1
Figure 9. An Example of a Block Write^[8]
byte count may not be 0. A block write command is allowed to
Serial Data Interface
transfer a maximum of 32 data bytes. The slave receiver
address for W254B is 11010010. Figure 9 shows an example
The W254B features a two-pin, serial data interface that can ^{of a block write.}
be used to configure internal register settings that control
particular device functions.
The command code and the byte count bytes are required as
the first two bytes of any transfer. W254B expects a command
Data Protocol
code of 0000 0000. The byte count byte is the number of
additional bytes required for the transfer, not counting the
The clock driver serial protocol accepts only block writes from command code and byte count bytes. Additionally, the byte
the controller. The bytes must be accessed in sequential order count byte is required to be a minimum of 1 byte and a
from lowest to highest byte with the ability to stop after any maximum of 32 bytes to satisfy the above requirement. Table
complete byte has been transferred. Indexed bytes are not 10 shows an example of a possible byte count value.
allowed.
A transfer is considered valid after the acknowledge bit corre-
A block write begins with a slave address and a write condition. sponding to the byte count is read by the controller. The
After the command code the core logic issues a byte count command code and byte count bytes are ignored by the
which describes how many more bytes will follow in the W254B. However, these bytes must be included in the data
message. If the host had 20 bytes to send, the first byte would write sequence to maintain proper byte allocation.
be the number 20 (14h), followed by the 20 bytes of data. The
Table 10.Example of Possible Byte Count Value
Byte Count Byte
MSB
LSB
0000
0000
0000
0001
0000
0010
0000
0011
0000
0100
0000
0101
0000
0110
Notes
Not allowed. Must have at least one byte
Data for functional and frequency select register (currently byte 0 in spec)
Writes first two bytes of data (byte 0 then byte 1)
Writes first three bytes (byte 0, 1, 2 in order)
Writes first four bytes (byte 0, 1, 2, 3 in order)
Writes first five bytes (byte 0, 1, 2, 3, 4 in order)
Writes first six bytes (byte 0, 1, 2, 3, 4, 5 in order)
0000
0010
0111
0000
Writes first seven bytes (byte 0, 1, 2, 3, 4, 5, 6 in order)
Max. byte count supported = 32
W254B Serial Configuration Map
1. The serial bits will be read by the clock driver in the following
order:
Byte 0 - Bits 7, 6, 5, 4, 3, 2, 1, 0
Byte 1 - Bits 7, 6, 5, 4, 3, 2, 1, 0
Byte N - Bits 7, 6, 5, 4, 3, 2, 1, 0
Note:
8. The acknowledgment bit is returned by the slave/receiver (W254B).
2. All unused register bits (reserved and N/A) should be
written to a “0” level.
• All register bits labeled “Initialize to 0" must be written to
zero during initialization. Failure to do so may result in higher
than normal operating current.
Rev 1.0, November 20, 2006
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