TC1784
System Control Unit (SCU)
User´s Manual
3-55
V1.1, 2011-05
32-bit SCU, V1.18
Fractional divider Mode
When the Fractional Divider Mode is selected (MOD_FDR.DM = 10
B
), the module clock
f
MOD
is derived from the bus clock
f
CLC
by division of a fraction of n/1024 for any value of
n from 0 to 1023. In general, the Fractional Divider Mode makes it possible to program
the average module clock frequency with a higher accuracy than in Normal Divider
Mode.
In Fractional Divider Mode, an clock pulse at
f
MOD
is generated depending on the result
of the addition MOD_FDR. MOD_FDR.STEP. If the addition leads to an
overflow over 3FF
H
, a pulse is generated at
f
MOD
. Note that in Fractional Divider Mode
the clock
f
MOD
can have a maximum period jitter of one
f
CLC
clock period.
The frequencies in Fractional Divider Mode are defined according to the following
formula:
, with n = 0-1023
(3.18)
Note: Each write to register FDR with bit field DM = 01
B
or 10
B
sets bit field RESULT to
3FF
H
.
Suspend Mode
The operation of the fractional divider can be controlled by the Suspend Mode Request
input. This input is activated in Suspend Mode by the on-chip debug control logic. In
Suspend Mode, module registers are accessible for read and write actions, but other
module internal functions are frozen.
The state of the Suspend Mode Request and Suspend Mode Acknowledge is latched in
two status flags of register MOD_FDR, SUSREQ and SUSACK. Suspend Mode Request
and (Suspend Mode Acknowledge or bit SM) must remain set both to maintain the
Suspend Mode.
The Kernel Disable Request becomes always active when the Module Disable Request
signal is activated, independently of the Suspend Mode settings in the fractional divider.
External Clock Enable
When the module clock generation has been disabled by software (setting
MOD_FDR.DISCLK = 1), the disable state can be exited when the External Clock
Enable input = 1. This feature is enabled when MOD_FDR.ENHW = 1.
f
MOD
f
CLC
n
1024
-------------
×
=
Содержание TC1784
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