LM3S8938 Datasheet, PDF (75/550 Pages) List of Unclassifed Manufacturers – Microcontroller

LM3S8938 Microcontroller
Bit/Field
11
10
9:6
5:4
Name
BYPASS
reserved
XTAL
OSCSRC
Type
R/W
RO
R/W
R/W
Reset
1
0
0xB
0x1
Description
PLL Bypass
Chooses whether the system clock is derived from the PLL output or
the OSC source. If set, the clock that drives the system is the OSC
source. Otherwise, the clock that drives the system is the PLL output
clock divided by the system divider.
Note:
The ADC must be clocked from the PLL or directly from a
14-MHz to 18-MHz clock source to operate properly. While
the ADC works in a 14-18 MHz range, to maintain a 1 M
sample/second rate, the ADC must be provided a 16-MHz
clock source.
Software should not rely on the value of a reserved bit. To provide
compatibility with future products, the value of a reserved bit should be
preserved across a read-modify-write operation.
This field specifies the crystal value attached to the main oscillator. The
encoding for this field is provided in Table 6-3 on page 75.
Picks among the four input sources for the OSC. The values are:
Value Input Source
00 Main oscillator (default)
01 Internal oscillator (default)
10 Internal oscillator / 4 (this is necessary if used as input to PLL)
11 reserved
3:2
reserved
RO
0x0
Software should not rely on the value of a reserved bit. To provide
compatibility with future products, the value of a reserved bit should be
preserved across a read-modify-write operation.
1
IOSCDIS
R/W
0
Internal Oscillator (IOSC) Disable
0: Internal oscillator is enabled.
1: Internal oscillator is disabled.
0
MOSCDIS
R/W
1
Main Oscillator Disable
0: Main oscillator is enabled.
1: Main oscillator is disabled (default).
Table 6-3. Default Crystal Field Values and PLL Programming
Crystal Number (XTAL Binary Value) Crystal Frequency (MHz) Not Using Crystal Frequency (MHz) Using the PLL
the PLL
0000
1.000
reserved
0001
1.8432
reserved
0010
2.000
reserved
0011
2.4576
reserved
0100
3.579545 MHz
0101
3.6864 MHz
0110
4 MHz
0111
4.096 MHz
June 14, 2007
75
Luminary Micro Confidential-Advance Product Information