CY28331
Document #: 38-07491 Rev. *E
Page 5 of 17
Byte 2: USB, 24–48MHz, REF(0:2) Control Register
Bit
@Pup
Pin #
Name
Description
7
active = 1
37, 36
CPUT/C(1) CPUT/C(1) shutdown. This bit can be optionally used to disable the CPUT/C(1)
clock pair. During shutdown, CPUT = low and CPUC = high
6
active = 1
41, 40
CPUT/C(0) CPUT/C(0) shutdown. This bit can be optionally used to disable the CPUT/C(0)
clock pair. During shutdown, CPUT = low and CPUC = high
5
active = 1
45
REF2
Enable (1 = Enabled, 0 = Disabled)
4
active = 1
48
REF1
Enable (1 = Enabled, 0 = Disabled)
3
active = 1
1
REF0
Enable (1 = Enabled, 0 = Disabled)
2
active = 1
28
24_48MHz Enable (1 = Enabled, 0 = Disabled)
1
active = 1
31
USB
Enable (1 = Enabled, 0 = Disabled)
0
0
For Test, always program to ‘0’
Byte 3: PCI Clock Free Running Select Control Register
Bit
@Pup
Pin #
Name
Description
7
Inactive = 0
PCI_DRV
0 = Low Strength
1 = High Strength
6
Inactive = 0
PCI33_HT66 Drive Strength
0 = Low Strength
1 = High Strength
5
Inactive = 0
22
PCI5
Free running enable (10 = Free running, 0 = Disabled)
4
Inactive = 0
21
PCI4
Free running enable (1 = Free running, 0 = Disabled)
3
Inactive = 0
18
PCI3
Free running enable (1 = Free running, 0 = Disabled)
2
1
11
PCI33_HT66_3 Enable (1 = Enabled, 0 = Disabled)
1
1
8
PCI33_HT66_2 Enable (1 = Enabled, 0 = Disabled)
0
1
7
PCI33_HT66_1 Enable (1 = Enabled, 0 = Disabled)
Byte 4: Pin Latched/Real-time State
Bit
@Pup
Pin#
Name
Description
7
1
6
PCI33_HT66_0
Enable (1 = Enabled, 0 = Disabled)
6
HW
24_48MHz/SEL# Pin power-up latched state
5
0
Reserved
For Test, always program to ‘0’
4
1
SSEN
Spread Spectrum enable (0 = disable, 1 = enable).
This bit provides a SW programmable control for spread spectrum clocking.
3
FS3 pin
31
FS3
Power-up latched state
2
FS2 pin
45
FS2
Power-up latched state
1
FS1 pin
48
FS1
Power-up latched state
0
FS0 pin
1
FS0
Power-up latched state
Byte 5: SSCG, Dial-a-Skew™, and Dial-a-Ratio™ Register
Bit
@Pup
Description
7
0
Spread Spectrum Selection:
bit7
bit6
bit5
% Spread
0
0
0
–1.5
0
0
1
–1.0
0
1
0
–0.7
0
1
1
–0.5 (default)
1
0
0
±0.75
1
0
1
±0.50
1
1
0
±0.35
1
1
1
±0.25
61
51
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