LM3S328 Datasheet, PDF (60/371 Pages) List of Unclassifed Manufacturers – Microcontroller

System Control
6.2 Initialization and Configuration
The PLL is configured using direct register writes to the Run-Mode Clock Configuration (RCC)
register. The steps required to successfully change the PLL-based system clock are:
1. Bypass the PLL and system clock divider by setting the BYPASS bit and clearing the USESYS
bit in the RCC register. This configures the system to run off a “raw” clock source (using the
main oscillator or internal oscillator) and allows for the new PLL configuration to be validated
before switching the system clock to the PLL.
2. Select the crystal value (XTAL) and oscillator source (OSCSRC), and clear the PWRDN and OEN
bits in RCC. Setting the XTAL field automatically pulls valid PLL configuration data for the
appropriate crystal, and clearing the PWRDN and OEN bits powers and enables the PLL and its
output.
3. Select the desired system divider (SYSDIV) and set the USESYS bit in RCC. The SYSDIV field
determines the system frequency for the microcontroller.
4. Wait for the PLL to lock by polling the PLLLRIS bit in the Raw Interrupt Status (RIS) register.
If the PLL doesn’t lock, the configuration is invalid.
5. Enable use of the PLL by clearing the BYPASS bit in RCC.
Important: If the BYPASS bit is cleared before the PLL locks, it is possible to render the device
unusable.
6.3 Register Map
Table 6-1 lists the System Control registers, grouped by function. The offset listed is a
hexadecimal increment to the register’s address, relative to the System Control base address of
0x400FE000.
Table 6-1. System Control Register Map
Offset Name
Reset
Type Description
See
page
Device Identification and Capabilities
0x000 DID0
-
RO Device identification 0
62
0x004 DID1
-
RO Device identification 1
63
0x008 DC0
0x000F0007
RO Device capabilities 0
65
0x010 DC1
0x00000007
RO Device capabilities 1
66
0x014 DC2
0x00071013
RO Device capabilities 2
68
0x018 DC3
0x3FFF0000
RO Device Capabilities 3
69
0x01C DC4
0x0000001F
RO Device Capabilities 4
71
Local Control
0x030 PBORCTL
0x00007FFD R/W Power-On and Brown-Out Reset Control
72
0x034 LDOPCTL
0x00000000 R/W LDO Power Control
73
0x040 SRCR0
0x00000000 R/W Software Reset Control 0
74
60
April 27, 2007
Preliminary