FMS7401 Fairchild Semiconductor, FMS7401 Datasheet - Page 11

• Manufacturer Part Number: FMS7401
• Description: Digital Power Controller
• Manufacturer: Fairchild Semiconductor

The FS[1:0] bits of the PSCALE register
changed by software at any time; however, if the PWM Timer 1 circuit is in run mode the FS[1:0] value will not change the
F
PWM cycle end time will dictate the divide factor of the F
the value reported will be the last value written by software (it may not necessarily reflect the divide factor for the current
PWM cycle).
The main system instruction clock (F
with the same divide factor as the FS[1:0] = 00 selection.
(if FMODE=1) or F
eight times faster than the standard. The FMODE bit may not be set if the PLL is not enabled.
FMODE while PLLEN=0 will force FMODE=0 ignoring any set instruction. Once the PLL has been enabled, software may
change F
In order to synchronously disable the PLL clocking structure, software must clear FSEL and FMODE before clearing the
PLLEN bit in order to disable the PLL successfully e.g. using separate instructions like “RBIT PLLEN, PSCALE.” There are
also special conditions for Halt/Idle power saving modes that must also be considered. Please refer to the
section of the datasheet for details.
REV. 1.0.3 1/24/05
PRODUCT SPECIFICATION
PWMCLK
C
ICLK
output frequency until after the PWM cycle ends (once the TMR1 counter overflows). The last FS[1:0] value at the
l o c k
O
I
n
s
’s source on-the-fly during normal instruction execution in order to speed-up a particular action.
I
t
N
c i l l a t o
T
e r
r
I
i
T
n
m m
2
a l
r
i
n
RCLK1
g
(
F
O
S
divided-by-2 signal. With the FMODE bit enabled, it is possible to execute instructions at a speed
C
)
F
R
C L K
1
D i
ICLK
b y 2
v
i
d e
4
) source may be provided by the internal oscillator (F
select the divide factor for the F
Figure 3. Internal Clock Scheme
R E
B
A
F
S e
Y
B Y
l
2
6
P L L
The FMODE bit of the PSCALE register
PWMCLK
F
R
E N
C L K
2
F
F
S [ 1 ]
S [ 0 ]
output for the next PWM cycle. When reading the FS[1:0],
(
F
D i g i t a l
P L L
M
u
)
(
P L L
l t i
PWMCLK
C
p
l i
l o c k
)
e r
output (see
F
(
F
F
S
P W M C L K
= 0
)
5
Table
OSC
Any attempts to write to
B
A
F
S
) or the PLL’s F
S e
4
Y
E
l
selects between the F
F
L
3). The FS bits may be
M
O
D
Power Saving Modes
E
A
B
S e
l
Y
F
T
1
C L K
(FS=0)
F
I
C L K
FMS7401L
output
(FS=0)
11