CY28416
initialize 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.
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
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.
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
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)
FS_C
FS_B
FS_A
CPU
SRC
PCIF/PCI
33 MHz
33 MHz
33 MHz
33 MHz
33 MHz
REF0
DOT96
96 MHz
96 MHz
96 MHz
96 MHz
96 MHz
USB
1
0
0
0
0
1
1
1
0
0
1
1
0
0
1
1
1
1
1
0
0
0
0
1
100 MHz
133 MHz
166 MHz
200 MHz
266 MHz
100 MHz
100 MHz
100 MHz
100 MHz
100 MHz
14.318 MHz
14.318 MHz
14.318 MHz
14.318 MHz
14.318 MHz
48 MHz
48 MHz
48 MHz
48 MHz
48 MHz
RESERVED
T
Table 2. Command Code Definition
Bit
Description
7
0 = Block read or block write operation, 1 = Byte read or byte write operation
Byte offset for byte read or byte write operation. For block read or block write operations, these bits should be '0000000'
(6:0)
Table 3. Block Read and Block Write Protocol
Block Write Protocol
Block Read Protocol
Description
Bit
1
Description
Bit
1
Start
Start
8:2
9
Slave address – 7 bits
Write
8:2
9
Slave address – 7 bits
Write
10
Acknowledge from slave
Command Code – 8 Bits
Acknowledge from slave
10
Acknowledge from slave
Command Code – 8 Bits
Acknowledge from slave
Repeat start
18:11
19
18:11
19
27:20
Byte Count – 8 bits
(Skip this step if I2C_EN bit set)
20
28
36:29
37
Acknowledge from slave
Data byte 1 – 8 bits
27:21
28
Slave address – 7 bits
Read = 1
Acknowledge from slave
Data byte 2 – 8 bits
29
Acknowledge from slave
Byte Count from slave – 8 bits
45:38
37:30
Rev 1.0,November 22, 2006
Page 3 of 14
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