Functional Description
210
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
System Control
(1)
For all examples listed, Q = 0
(2)
For a given crystal frequency, N should be chosen such that the reference frequency is within 4 to 30
MHz.
Table 4-6. Actual PLL Frequency
(1)
Crystal
Frequency
(MHz)
MINT
N
Reference
Frequency
(MHz)
(2)
PLL Frequency
(MHz)
(Decimal)
(Hex)
5
64
0x40
0x0
5
320
6
160
0x35
0x2
2
320
8
40
0x28
0x0
8
320
10
32
0x20
0x0
10
320
12
80
0x50
0x2
4
320
16
20
0x14
0x0
16
320
18
160
0xA0
0x8
2
320
20
16
0x10
0x0
20
320
24
40
0x28
0x2
8
320
25
64
0x40
0x4
5
320
5
96
0x60
0x0
5
480
6
80
0x50
0x0
6
480
8
60
0x3C
0x0
8
480
10
48
0x30
0x0
10
480
12
40
0x28
0x0
12
480
16
30
0x1E
0x0
16
480
18
80
0x50
0x2
6
480
20
24
0x18
0x0
20
480
24
20
0x14
0x0
24
480
25
96
0x60
0x4
5
480
4.1.5.5.2 PLL Operation
If a PLL configuration is changed, the PLL output frequency is unstable until it reconverges (relocks) to the
new setting. The time between the configuration change and relock is t
READY
(see the device-specific data
sheet). During the relock time, the affected PLL is not usable as a clock reference. Software can poll the
LOCK bit in the PLL Status (PLLSTAT) register to determine when the PLL has locked.
Do not modify the PLL VCO frequency while the PLL serves as a clock source to the system. All changes
to the PLL must be performed using a different clock source until the PLL has locked frequency. Thus,
changing the PLL VCO frequency must be done as a sequence from the PLL to PIOSC or MOSC and
then PIOSC or MOSC to the new PLL.
Hardware is provided to keep the PLL from being used as a system clock until the t
READY
condition is met
after one of the previous changes. Software must ensure that the system is using a stable clock source
(like the main oscillator) before the RSCLKCFG register is reprogrammed to enable the PLL. Software can
use many methods to ensure that the system is clocked from the PLL, including periodically polling the
PLLLRIS bit in the RIS register at offset 0x050, and enabling the PLL Lock interrupt in the IMC register at
offset 0x054.
4.1.6 System Control
Four levels of operation are defined for the microcontroller:
•
Run mode (see
•
Sleep mode (see
)
•
Deep-sleep mode (see
•
Hibernation mode (see