
System Control Registers
237
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
System Control
4.2.10 MOSCCTL Register (Offset = 0x7C) [reset = 0xC]
Main Oscillator Control (MOSCCTL)
This register provides control over the features of the main oscillator, including the ability to enable the
MOSC clock verification circuit, what action to take when the MOSC fails, and whether or not a crystal is
connected. When enabled, this circuit monitors the frequency of the MOSC to verify that the oscillator is
operating within specified limits. If the clock goes invalid after being enabled, the microcontroller issues a
power-on reset and reboots to the NMI handler or generates an interrupt.
NOTE:
If the MOSC is chosen as the clock to the Ethernet PHY then software must enable the
MOSC before enabling the Ethernet PHY by setting the P0 bit in the PCEPHY.
MOSCCTL is shown in
and described in
Return to
Figure 4-16. MOSCCTL Register
31
30
29
28
27
26
25
24
RESERVED
R-0x0
23
22
21
20
19
18
17
16
RESERVED
R-0x0
15
14
13
12
11
10
9
8
RESERVED
R-0x0
7
6
5
4
3
2
1
0
RESERVED
OSCRNG
PWRDN
NOXTAL
MOSCIM
CVAL
R-0x0
R/W-0x0
R/W-0x1
R/W-0x1
R/W-0x0
R/W-0x0
Table 4-20. MOSCCTL Register Field Descriptions
Bit
Field
Type
Reset
Description
31-5
RESERVED
R
0x0
4
OSCRNG
R/W
0x0
Oscillator Range
Specifies the frequency range of operation of the oscillator.
0x0 = Low-frequency range
0x1 = High-frequency range (equal to or greater than 10 MHz).
3
PWRDN
R/W
0x1
Power Down
Provides user control over powering down the main oscillator circuit.
This bit should be cleared when using a crystal and set for single-
ended mode.
0x0 = Power to MOSC circuit is enabled.
0x1 = MOSC circuit is powered down.
2
NOXTAL
R/W
0x1
No MOSC or Crystal Connected
Provides the user control over the power drawn from the main
oscillator circuit. This bit should be set when either crystal or single-
ended mode is being used. If the application needs MOSC, this bit
should be cleared.
0x0 = This bit should be cleared when a crystal or oscillator is
connected to the OSC0 and OSC1 inputs, regardless of whether or
not the MOSC is used or powered down. For proper clock
functionality when switching to crystal mode, software must clear this
bit and set the PWRDN bit in a single write access.
0x1 = This bit should be set when a crystal or external oscillator is
not connected to the OSC0 and OSC1 inputs to reduce power
consumption.