145
Clock Generator
Chapter 4
Preliminary User’s Manual U17566EE1V2UM00
(1)
SCFC0 - SSCG frequency control register 0
The 8-bit SCFC0 register controls the frequency modulation of the SSCG. It
determines the SSCG output frequency and is used in conjunction with
register SCFC1.
The center SSCG output frequency is f
SSCGc
= (4 MHz
×
N/M) / 2. This
register defines the divisor “m” and thus M = m + 1.
Access
This register can be read/written in 8-bit or 1-bit units.
Address
FFFF F82C
H
.
Initial Value
52
H
. The register is initialized by any reset.
Note
1.
This register can only be rewritten with a new value if the SSCG is
switched off. Refer to the explanation at the beginning of this section.
2.
The inital value of this register must be changed after reset.
Frequency
calculation
If dithering mode is disabled (CKC.DEN = 0) the SSCG outputs it’s center
frequency f
SSCGc
:
f
SSCGc
= (4 MHz x N/M) / 2
where:
• M = m + 1 = SCFC0.SCFC0[2:0] + 1
• N = n + 1 = SCFC1.SCFC1[6:0] + 1
The values to be written into SCFC0 and SCFC1 are restricted. Possible
combinations are:
7
6
5
4
3
2
1
0
0
a
a)
The default value “0” of this bit must not be altered.
SCFC06
SCFC05
SCFC04
SCFC03
SCFC02
SCFC01
SCFC00
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Table 4-8
SCFC0 register contents
Bit position
Bit name
Function
6 to 5
SCFC0[6:5]
Must be set to 01
B
4 to 3
SCFC0[4:3]
Must be set according to
Table 4-9
2 to 0
SCFC0[2:0]
Determines the divisor m
Table 4-9
Supported settings of N (n) and M (m)
f
SSCGmax
M (m)
N (n)
SCFC0
SCFC1
48 MHz
4 (3)
96 (95)
2B
H
DF
H
64 MHz
a
a)
In this mode the 64 MHz SSCG output frequency has to be devided by the SSCG
post scaler. Thus set SCPS = 21
H
for 32 MHz or SCPS = 23
H
for 16 MHz opera-
tion.
3 (2)
96 (95)
32
H
DF
H
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