CY28RS400
Document #: 38-07637 Rev. *B Page 3 of 19
Frequency Select Pins (FS_A, FS_B, FS_C and
409_410)
Host clock frequency selection is achieved by applying the
appropriate logic levels to FS_A, FS_B, FS_C and 409_410
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, FS_C and 409_410 input
values. For all logic levels of FS_A, FS_B, FS_C and 409_410
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, FS_C and 409-410 transitions
will be ignored. There are 2 CPU frequency select tables. One
based on the CK409 specifications and one based on the
CK410 specifications. The table to be used is determined by
the value latched on the PCI0/409_410 pin by the
VTT_PWRGD/PD# pin. A '0' on this pin selects the 410
frequency table and a '1' on this pin selects the 409 frequency
table. In the 409 table, only the FS_A and FS_B pins influence
the frequency selection.
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 3.
The block write and block read protocol is outlined in Table 4
while Table 5 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) 410 mode, 409_410 = 0
FS_C FS_B FS_A CPU SRC PCIF/PCI REF0 USB
1 0 1 100 MHz 100 MHz 33 MHz 14.318 MHz 48 MHz
0 0 1 133 MHz 100 MHz 33 MHz 14.318 MHz 48 MHz
0 1 0 200 MHz 100 MHz 33 MHz 14.318 MHz 48 MHz
0 0 0 266 MHz 100 MHz 33 MHz 14.318 MHz 48 MHz
1 1 1 Reserved 100 MHz 33 MHz 14.318 MHz 48 MHz
Table 2. Frequency Select Table (FS_A FS_B) 410 mode, 409_410 = 1
FS_B FS_A CPU SRC PCIF/PCI REF0 USB
0 0 100 MHz 100 MHz 33 MHz 14.318 MHz 48 MHz
0 1 133 MHz 100 MHz 33 MHz 14.318 MHz 48 MHz
1 0 200 MHz 100 MHz 33 MHz 14.318 MHz 48 MHz
Table 3. Command Code Definition
Bit Description
7 0 = Block read or block write operation, 1 = Byte read or byte write operation
(6:5) Chip select address, set to ‘00’ to access device
(4:0) Byte offset for byte read or byte write operation. For block read or block write operations, these bits should be '00000'
Table 4. Block Read and Block Write Protocol
Block Write Protocol Block Read Protocol
Bit Description Bit Description
1 Start 1 Start
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
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