........................Document #: 38-07594 Rev. *B Page 3 of 18
Frequency Select Pins (FS_A, FS_B and FS_C)
Host clock frequency selection is achieved by applying the
appropriate logic levels to FS_A, FS_B, FS_C inputs prior to
VTT_PWRGD# assertion (as seen by the clock synthesizer).
Upon VTT_PWRGD# being sampled low by the clock chip
(indicating processor VTT voltage is stable), the clock chip
samples the FS_A, FS_B and FS_C input values. For all logic
levels of FS_A, FS_B and FS_C, VTT_PWRGD# employs a
one-shot functionality in that once a valid low on
VTT_PWRGD# has been sampled, all further VTT_PWRGD#,
FS_A, FS_B and FS_C transitions will be ignored, except in
test mode.
Serial Data Interface
To enhance the flexibility and function of the clock synthesizer,
a two-signal serial interface is provided. Through the Serial
Data Interface, various device functions, such as individual
clock output buffers, can be individually enabled or disabled.
The registers associated with the Serial Data Interface
initializes to their default setting upon power-up, and therefore
use of this interface is optional. Clock device register changes
are normally made upon system initialization, if any are
required. The interface cannot be used during system
operation for power management functions.
Data Protocol
The clock driver serial protocol accepts byte write, byte read,
block write, and block read operations from the controller. For
block write/read operation, the bytes must be accessed in
sequential order from lowest to highest byte (most significant
bit first) with the ability to stop after any complete byte has
been transferred. For byte write and byte read operations, the
system controller can access individually indexed bytes. The
offset of the indexed byte is encoded in the command code,
as described in Table 2.
The block write and block read protocol is outlined in Table 3
while Table 4 outlines the corresponding byte write and byte
read protocol. The slave receiver address is 11010010 (D2h).
Table 1. Frequency Select Table FS_A, FS_B and FS_C
FS_C FS_B FS_A CPU SRC PCIF/PCI REF0 DOT96 USB
MID 0 1 100 MHz 100 MHz 33 MHz 14.318 MHz 96 MHz 48 MHz
0 0 1 133 MHz 100 MHz 33 MHz 14.318 MHz 96 MHz 48 MHz
011
RESERVED
010
000
MID 0 0
MID 1 0
MID 1 1
1 0 x Hi-Z Hi-Z Hi-Z Hi-Z Hi-Z Hi-Z
1 1 0 REF/2 REF/8 REF/24 REF REF REF
1 1 1 REF/2 REF/8 REF/24 REF REF REF
Table 2. Command Code Definition
Bit Description
7 0 = Block read or block write operation, 1 = Byte read or byte write operation
(6:0) Byte offset for byte read or byte write operation. For block read or block write operations, these bits should be
'0000000'
Table 3. Block Read and Block Write Protocol
Block Write Protocol Block Read Protocol
Bit Description Bit Description
1Start 1Start
8:2 Slave address – 7 bits 8:2 Slave address – 7 bits
9 Write 9 Write
10 Acknowledge from slave 10 Acknowledge from slave
18:11 Command Code – 8 bits 18:11 Command Code – 8 bits
19 Acknowledge from slave 19 Acknowledge from slave
27:20 Byte Count – 8 bits
(Skip this step if I
2
C_EN bit set)
20 Repeat start
