TC1796
System Units (Vol. 1 of 2)
Clock System and Control
User’s Manual 3-32 V2.0, 2007-07
Clock, V2.0
3.3.3.2 Fractional Divider Operating Modes
The fractional divider has two operating modes:
• Normal divider mode
• Fractional divider mode
Normal Divider Mode
In normal divider mode (FDR.DM = 01
B
), the fractional divider behaves as a reload
counter (addition of +1) that generates an output clock pulse at f
OUT
on the transition from
3FF
H
to 000
H
. FDR.RESULT represents the counter value and FDR.STEP determines
the reload value.
The output frequencies in normal divider mode are defined according to the following
formulas:
(3.5)
In order to get
f
OUT
= f
IN
STEP must be programmed with 3FF
H
. Figure 3-7 shows the
operation of the normal divider mode with a reload value of FDR.STEP = 3FD
H
. The
clock signal f
OUT
is the AND combination of the f
OUT
Enable signal with f
IN
.
Figure 3-7 Normal Mode Timing
f
OUT
f
IN
1
n
---×=
, with n = 1024 - STEP
MCT05605
RESULT 3FF
f
IN
3FE3FD 3FF 3FD3FD 3FE 3FF
3FD
3FE
STEP
Reload
3FD
Reload
3FD
Reload
f
OUT
Enable
f
OUT
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