System and Peripheral Control Registers
195
SPNU563A – March 2018
Copyright © 2018, Texas Instruments Incorporated
Architecture
2.5.1.42 Clock Control Register (CLKCNTL)
The CLKCNTL register, shown in
and described in
, controls peripheral reset and
the peripheral clock divide ratios.
NOTE:
VCLK and VCLK2 clock ratio restrictions.
The VCLK2 frequency must always be greater than or equal to the VCLK frequency. The
VCLK2 frequency must be an integer multiple of the VCLK frequency.
In addition, the VCLK and VCLK2 clock ratios must not be changed simultaneously. When
increasing the frequency (decreasing the divider), first change the VCLK2R field and then
change the VCLKR field. When reducing the frequency (increasing the divider), first change
the VCLKR field and then change the VCLK2R field.
You should do a read-back between the two writes. This assures that there are enough clock
cycles between the two writes.
Figure 2-49. Clock Control Register (CLKCNTL) (offset = D0h)
31
28
27
24
23
20
19
16
Reserved
VCLK2R
Reserved
VCLKR
R-0
R/WP-1h
R-0
R/WP-1h
15
9
8
7
0
Reserved
PENA
Reserved
R-0
R/WP-0
R-0
LEGEND: R/W = Read/Write; R = Read only; WP = Write in privileged mode only; -
n
= value after reset
Table 2-61. Clock Control Register (CLKCNTL) Field Descriptions
Bit
Field
Value
Description
31-28
Reserved
0
Reads return 0. Writes have no effect.
27-24
VCLK2R
VBUS clock2 ratio.
Note: The VCLK2 frequency must always be greater than or equal to the VCLK frequency.
The VCLK2 frequency must be an integer multiple of the VCLK frequency. In addition, the
VCLK and VCLK2 clock ratios must not be changed simultaneously.
0
The VCLK2 speed is HCLK divided by 1.
:
:
Fh
The VCLK2 speed is HCLK divided by 16.
23-20
Reserved
0
Reads return 0. Writes have no effect.
19-16
VCLKR
VBUS clock ratio.
Note: The VCLK2 frequency must always be greater than or equal to the VCLK frequency.
The VCLK2 frequency must be an integer multiple of the VCLK frequency. In addition, the
VCLK and VCLK2 clock ratios must not be changed simultaneously.
0
The VCLK speed is HCLK divided by 1.
:
:
Fh
The VCLK speed is HCLK divided by 16.
15-9
Reserved
0
Reads return 0. Writes have no effect.
8
PENA
Peripheral enable bit. The application must set this bit before accessing any peripheral.
0
The global peripheral/peripheral memory frames are in reset.
1
All peripheral/peripheral memory frames are out of reset.
7-0
Reserved
0
Reads return 0. Writes have no effect.