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SCALER RATIOS
Master Mode bit MM15 controls the counting configuration of the
Frequency Scaler
counter~
When MM15
=
0, the Scaler divides the
oscillator frequency in binary steps so that each subfrequency is 1/16
of the preceding frequency.
When MM15
=
1, the Scaler divides in BCD
steps so that adjacent frequencies are related by ratios of 10 instead
of 16.
FRE()UENCY SCAL.ING GOUNTER
A 16-bit scaling counter divides the output of the on-chip oscillator
into four additional sub-frequencies.
This provides a total of five
internal frequencies that can be routed to any of the general counters
and to the FOUT divider.
The scaler is tapped every four bits and can
be programmed to divide in binary or in BCD.
The combinations of
frequencies thus available are shown in figure 3-15.
For example, if
the base oscillator frequency is 8fVlHz, the F4 frequency will be 8KHz
when BCD seal i ng is sel ected.
If the base osci
11
ator frequency is
8MHz, the F3 frequency wi
11
be 31.25KHz when bi na ry sea
1
i ng is
selected.
The control bit that selects BCD or binary scaling is
located in the Master Mode register.
- - - - - - - - - -__ Fl
X l _
X 2 _
OSC
£
F2
F3
Fe
- - 0 - - - - ; 1
t=G~ ,.~"
L -
o
~
FREQUENCV SCALER
FO,equency
F1
F2
F3
F4
F5
BCD
Scaling
MM15
=
1
esc
F1 -;- 10
F1 -;- 100
F1 -;- 1,000
F1 -;- 10,000
Binary
Scaling
MM15
=
0
esc
F1 -;- 16
F1 -;- 256
F1 -;- 4,096
F1 -;- 65,536
Figure 3-15.
Frequency Scaler Ratios
3-23
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