W254B Datasheet, PDF (8/17 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]
Serial Data Interface
The W254B features a two-pin, serial data interface that can
be used to configure internal register settings that control par-
ticular device functions.
Data Protocol
The clock driver serial protocol accepts only block writes from
the controller. The bytes must be accessed in sequential order
from lowest to highest byte with the ability to stop after any
complete byte has been transferred. Indexed bytes are not
allowed.
A block write begins with a slave address and a write condition.
After the command code the core logic issues a byte count
which describes how many more bytes will follow in the mes-
sage. If the host had 20 bytes to send, the first byte would be
the number 20 (14h), followed by the 20 bytes of data. The
byte count may not be 0. A block write command is allowed to
transfer a maximum of 32 data bytes. The slave receiver ad-
dress for W254B is 11010010. Figure 9 shows an example of
a block write.
The command code and the byte count bytes are required as
the first two bytes of any transfer. W254B expects a command
code of 0000 0000. The byte count byte is the number of ad-
ditional bytes required for the transfer, not counting the com-
mand code and byte count bytes. Additionally, the byte count
byte is required to be a minimum of 1 byte and a maximum of
32 bytes to satisfy the above requirement. Table 8 shows an
example of a possible byte count value.
A transfer is considered valid after the acknowledge bit corre-
sponding to the byte count is read by the controller. The com-
mand code and byte count bytes are ignored by the W254B.
However, these bytes must be included in the data write se-
quence to maintain proper byte allocation.
Table 8. Example of Possible Byte Count Value
Byte Count Byte
Notes
MSB
LSB
0000
0000
Not allowed. Must have at least one byte
0000
0001
Data for functional and frequency select register (currently byte 0 in spec)
0000
0010
Writes first two bytes of data (byte 0 then byte 1)
0000
0011
Writes first three bytes (byte 0, 1, 2 in order)
0000
0100
Writes first four bytes (byte 0, 1, 2, 3 in order)
0000
0101
Writes first five bytes (byte 0, 1, 2, 3, 4 in order)
0000
0110
Writes first six bytes (byte 0, 1, 2, 3, 4, 5 in order)
0000
0111
Writes first seven bytes (byte 0, 1, 2, 3, 4, 5, 6 in order)
0010
0000
Max. byte count supported = 32
Note:
8. The acknowledgment bit is returned by the slave/receiver (W254B).
Document #: 38-07233 Rev. *A
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