Texas Instruments C28 Series, Student Manual

Page: 81 / 342

Oscillator/PLL Clock Module
Oscillator/PLL Clock Module
C28x Oscillator / PLL Clock Module
C28x Oscillator / PLL Clock Module
PLLCR @ 0x007021
PLLCR @ 0x007021
(lab file: (lab file: SysCtrl SysCtrl .c) .c)
DIV3 DIV2 DIV1 DIV0
DIV3 DIV2 DIV1 DIV0
Clock Frequency (CLKIN)
Clock Frequency (CLKIN)
0 0 0 0 0 0 0 0 OSCCLK x 1 / 2 (no PLL) * OSCCLK x 1 / 2 (no PLL) *
0 0 0 1
0 0 0 1
OSCCLK x 1 / 2
OSCCLK x 1 / 2
0 0 1 0 0 0 1 0 OSCCLK x 2 / 2 OSCCLK x 2 / 2
0 0 1 1 0 0 1 1 OSCCLK x 3 / 2 OSCCLK x 3 / 2
0 1 0 0 0 1 0 0 OSCCLK x 4 / 2 OSCCLK x 4 / 2
0 1 0 1 0 1 0 1 OSCCLK x 5 / 2 OSCCLK x 5 / 2
0 1 1 0
0 1 1 0
OSCCLK x 6 / 2
OSCCLK x 6 / 2
0 1 1 1 0 1 1 1 OSCCLK x 7 / 2 OSCCLK x 7 / 2
1 0 0 0
1 0 0 0
OSCCLK x 8 / 2
OSCCLK x 8 / 2
1 0 0 1 1 0 0 1 OSCCLK x 9 / 2 OSCCLK x 9 / 2
1 0 1 0 1 0 1 0 OSCCLK x 10 / 2 OSCCLK x 10 / 2
PLLCR
PLLCR
bits 15:4 bits 15:4
reserved
reserved
crystal crystal
PLL
PLL
Clock Module
Clock Module
4 4 - - bit PLL Select bit PLL Select
X1 /CLKIN X1 /CLKIN
X2 X2
XT
A
L
O
SC
XT
AL O
SC
Watchdog
Watchdog
Module
Module
/2 /2
PLLCLK PLLCLK
OSCCLK OSCCLK
•
•
C28x
C28x
Core Core
CLKIN
CLKIN
MUX
MUX
XF_XPLLDIS XF_XPLLDIS
0
0
1 1
SYSCLKOUT SYSCLKOUT
HISPCP
HISPCP
LOSPCP
LOSPCP
HSPCLK
HSPCLK
LSPCLK
LSPCLK
•
•
•
•
* default * default
The OSC/PLL clock module provides all the necessary clocking signals for C28x devices. The
PLL has a 4-bit ratio control to select different CPU clock rates. Two modes of operation are
supported – crystal operation, and external clock source operation. Crystal operation allows the
use of an external crystal/resonator to provide the time base to the device. External clock source
operation allows the internal oscillator to be bypassed, and the device clocks are generated from
an external clock source input on the X1/CLKIN pin. The watchdog receives a clock signal from
OSCCLK. The C28x core provides a SYSCLKOUT clock signal. This signal is prescaled to
provide a clock source for the on-chip peripherals through the high-speed and low-speed
peripheral clock prescalers.
C28x - System Initialization 5 - 3