TC1784
System Control Unit (SCU)
User´s Manual
3-28
V1.1, 2011-05
32-bit SCU, V1.18
The output frequencies in Normal Divider Mode are defined according to the following
formulas:
(3.14)
In order to get
f
OUT
=
f
FPI
/2 STEP must be programmed with 3FF
H
.
Fractional Divider Mode
When the Fractional Divider Mode is selected (FDR.DM = 10
B
), the output is derived
from the input clock
f
FPI
by division of a fraction of n/1024 for any value of n from 0 to
1023 followed by the division of two. In general, the Fractional Divider Mode makes it
possible to program the average output clock frequency with a higher accuracy than in
Normal Divider Mode.
In Fractional Divider Mode, a pulse is generated depending on the result of the addition
FDR. FDR.STEP. If the addition leads to an overflow over 3FF
H
, a pulse is
generated for the divider by two. Note that in Fractional Divider Mode the clock
f
OUT
can
have a maximum period jitter of one
f
FPI
clock period.
The output frequencies in Fractional Divider Mode are defined according to the following
formulas:
, with n = 0-1023
(3.15)
External Clock Enable
When the external clock generation with the fractional divider has been disabled by
software (setting FDR.DISCLK = 1), the disable state can be exited (hardware
controlled) when the External Clock Enable input = 1.
Programmable Frequency Output for EXTCLK1
f
OUT
f
FPI
1
n
---
×
2
-------------------
=
, with n = 1024 - STEP
f
OUT
f
FPI
n
1024
-------------
×
2
-----------------------------
=
Содержание TC1784
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