ICS9148-58 Datasheet, PDF (4/14 Pages) Integrated Circuit Systems – Frequency Generator & Integrated Buffers for PENTIUM/ProTM

ICS9148 - 58
General I²C 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:
Clock Generator
Address (7 bits)
A(6:0) & R/W#
D2(H)
+ 8 bits
ACK
dummy
ACK
command code
+ 8 bits
dummy Byte
count
ACK
Data Byte
1
ACK
Data Byte
N
ACK
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:
Clock Generator
Address (7 bits)
A(6:0) & R/W#
D3(H)
ACK
Byte
C ount
ACK
Data Byte
1
ACK
Data Byte
N
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.
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
I²C is a trademark of Philips Corporation
Serial Configuration Command Bitmap
Byte0: Functionality and Frequency Select Register
(default = 0)
Bit
Description
Bit 7 Reserved
Bit6 Bit5 CPU Clock PCI AGP
Bit4
111
100.2
33.3 66.6
110
95.25 31.75 63.5
Bit
101
83.3
33.3 66.6
6:4
100
133.3
44.3 88.7
011
75
37.5
75
010
124
41.3 82.7
001
66.8
33.4 66.8
000
112
37.3 74.7
0 - Frequency is selected by hardware select,
Bit 3 Latched Inputs
1 - Frequency is selected by Bit 6:4 (above)
Bit 2
0 - Spread Spectrum center spread type. ±.25%
1 - Spread Spectrum down spread type. 0 to -.5%
Bit 1
0 - Normal
1 - Spread Spectrum Enabled
Bit 0
0 - Running
1- Tristate all outputs
PWD
0
Note
1
0
0
0
0
4