MemoryMap Registers
108
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
Clock System (CS) Module
3.3.5 CTL4 Register (Offset = 8h) [reset = CDC9h]
CTL4 is shown in
and described in
.
Return to the
Clock System Control 4 Register
Figure 3-9. CTL4 Register
15
14
13
12
11
10
9
8
HFXTDRIVE
RESERVED
HFXTBYPASS
HFFREQ
RESERVED
HFXTOFF
R/W-3h
R-0h
R/W-0h
R/W-3h
R-0h
R/W-1h
7
6
5
4
3
2
1
0
LFXTDRIVE
RESERVED
LFXTBYPASS
VLOOFF
RESERVED
SMCLKOFF
LFXTOFF
R/W-3h
R-0h
R/W-0h
R/W-1h
R-0h
R/W-0h
R/W-1h
Table 3-8. CTL4 Register Field Descriptions
Bit
Field
Type
Reset
Description
15-14
HFXTDRIVE
R/W
3h
The HFXT oscillator current can be adjusted to its drive needs. This
in combination with the HFFREQ bits can be used for optimizing
crystal power based on crystal characteristics.
0h (R/W) = Lowest current consumption
1h (R/W) = Increased drive strength HFXT oscillator
2h (R/W) = Increased drive strength HFXT oscillator
3h (R/W) = Maximum drive strength HFXT oscillator
13
RESERVED
R
0h
Reserved. Always reads as 0.
12
HFXTBYPASS
R/W
0h
HFXT bypass select
0h (R/W) = HFXT sourced from external crystal
1h (R/W) = HFXT sourced from external clock signal
11-10
HFFREQ
R/W
3h
The HFXT frequency selection. These bits must be set to the
appropriate frequency for crystal or bypass modes of operation.
0h (R/W) = 0 to 4 MHz
1h (R/W) = Greater than 4 MHz to 8 MHz
2h (R/W) = Greater than 8 MHz to 16 MHz
3h (R/W) = Greater than 16 MHz to 24 MHz
9
RESERVED
R
0h
Reserved. Always reads as 0.
8
HFXTOFF
R/W
1h
Turns off the HFXT oscillator
0h (R/W) = HFXT is on if HFXT is selected via the port selection
and HFXT is not in bypass mode of operation
1h (R/W) = HFXT is off if it is not used as a source for ACLK,
MCLK, or SMCLK
7-6
LFXTDRIVE
R/W
3h
The LFXT oscillator current can be adjusted to its drive needs.
0h (R/W) = Lowest drive strength and current consumption LFXT
oscillator
1h (R/W) = Increased drive strength LFXT oscillator
2h (R/W) = Increased drive strength LFXT oscillator
3h (R/W) = Maximum drive strength and maximum current
consumption LFXT oscillator
5
RESERVED
R
0h
Reserved. Always reads as 0.
4
LFXTBYPASS
R/W
0h
LFXT bypass select
0h (R/W) = LFXT sourced from external crystal
1h (R/W) = LFXT sourced from external clock signal
3
VLOOFF
R/W
1h
VLO off. This bit turns off the VLO.
0h (R/W) = VLO is on
1h (R/W) = VLO is off if it is not used as a source for ACLK, MCLK,
or SMCLK or if not used as a source for the RTC in LPM3.5