4
ICS9148- 58
Byte0: Functionality and Frequency Select Register
(default = 0)
Serial Configuration Command Bitmap
Bit
Description
PWD
Bit 7 Reserved
0
Bit
6:4
Bit6 Bit5
Bit4
111
110
101
100
011
010
001
000
CPU Clock
100.2
95.25
83.3
133.3
75
124
66.8
112
PCI
33.3
31.75
33.3
44.3
37.5
41.3
33.4
37.3
AGP
66.6
63.5
66.6
88.7
75
82.7
66.8
74.7
Note
1
Bit 3
0 - Frequency is selected by hardware select,
Latched Inputs
1 - Frequency is selected by Bit 6:4 (above)
0
Bit 2
0 - Spread Spectrum center spread type. ±.25%
1 - Spread Spectrum down spread type. 0 to -.5%
0
Bit 1 0 - Normal
1 - Spread Spectrum Enabled
0
Bit 0
0 - Running
1- Tristate all outputs
0
General I
2C serial interface information
The information in this section assumes familiarity with I2C programming. For more information, contact ICS for an I2C
programming application note.
How to Write:
Send the address D2(H) .
Send two additional dummy bytes, a command code
and byte count.
Send the desired number of data bytes.
See the diagram below:
Note that the acknowledge bit is sent by the clock chip, and pulls the data line low. There is no minimum of data bytes that must
be sent.
How to Read:
Send the address D3(H).
Send the byte count in binary coded decimal
Read back the desired number of data bytes
See the diagram below:
The following specifications should be observed:
1.
Operating voltage for I2C pins is 3.3V
2.
Maximum data transfer rate (SCLK) is 100K bits/sec.
Clock Generator
Address (7 bits)
ACK
+ 8 bits
dummy
command code
ACK
+ 8 bits
dummy Byte
count
ACK
Data Byte
1
ACK
Data Byte
N
ACK
A(6:0) & R/W#
D2(H)
Clock Generator
Address (7 bits)
ACK
Byte
C ount
ACK
Data Byte
1
AC K
Data Byte
N
A(6:0) & R/W#
D3(H)
I2C is a trademark of Philips Corporation
Note 1. Default at Power-up will be for latched logic inputs
to define frequency. Bits 4, 5, 6 are default to 000,
and if bit 3 is written to a 1 to use Bits 6:4, then
these should be defined to desired frequency at same
write cycle.
Note: PWD = Power-Up Default