C9830
133 MHz Clock Generator for Intel 820 Chipset
Preliminary
Serial Control Registers (Cont.)
Byte 7: Frequency Stepping Register (1 = Enable, 0 =
Disable)
Byte 5: Control Register
Bit
@Pup
Pin#
Description
N1
N0, LSB
Select I²C programmability.
Sync_Out
Reserved
Reserved
Reserved
Reserved
Bit
7
@Pup Description
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
-
-
-
-
-
-
-
-
0
0
0
0
0
0
0
0
BW1, see table 2
6
5
BW0, see table 2
Reserved
4
Reserved
3
Reserved
2
Reserved
1
Reserved
0
Reserved
Byte 6: Frequency Stepping Register (1 = Enable, 0 =
Disable)
Bit
@Pup
Pin#
Description
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
-
-
-
-
-
-
-
-
N9, MSB
N8
N7
N6
N5
N4
N3
N2
Frequency Stepping Description
Frequency Stepping is a method for increasing the frequency of the output by the minimum possible step increase,
resolution. This device provides the ability to do so by programming the I2C registers Byte6 and Byte7. In order to enable
the Frequency Stepping feature, Byte 7, Bit 5 should be programmed to 1, and spread spectrum must be DISABLED,
Byte0, Bit1 set to 0. When entering the data into these registers, the user is actually programming a value that results in
a relative CPU output frequency following the formula below:
N
Fcpu = C1×
(MHz)
C2
Where: N is the value programmed into Bytes 6 and 7 (for the formula, use the Decimal N value, See Table 2)
C1 is a fixed constant 0.6225295652174
C2 is a constant set by the Sel133/100#, S(2:0) selection lines and displayed in the table below.
The N value may be programmed into the I2C in binary format MSB first. For example, if the user desires to enter an N
value of 323 then the following Binary equivalent value of “0101000011” should be entered MSB first.
Table 2 shows the default N values when the frequency is selected with Sel133/100#, S(2:0) select lines. It also shows
the max possible programmable frequency through frequency stepping, this maximum frequency is a result of a
maximum possible N value of 643.
The resolution is the minimum possible frequency increase relative to the minimum possible increase in the value of N, 1
LSB.
INTERNATIONAL MICROCIRCUITS, INC. 525 LOS COCHES ST
MILPITAS, CA 95035, USA TEL: 408-263-6300. FAX 408-263-6571
http://www.imicorp.com/
Rev 1.1
4/25/2000
Page 7 of 14
CYPRESS [ CYPRESS ]
