
Clock Module
7-4
Freescale Semiconductor
The clock module can operate in normal PLL mode with crystal reference, normal PLL mode with external
reference, and input clock limp mode.
7.1.3.1
Normal PLL Mode with Crystal Reference
In normal mode with a crystal reference, the PLL receives an input clock frequency from the crystal
oscillator circuit and multiplies the frequency to create the PLL output clock. It can synthesize frequencies
ranging from 22x to 33.75x the input frequency. The user must supply a crystal oscillator that is within the
appropriate input frequency range, the crystal manufacturer’s recommended external support circuitry, and
short signal route from the device to the crystal. In normal mode, the PLL can generate a dithered clock or
a non-dithered clock (locked on a single frequency). The dithering deviation, dither modulation frequency,
and whether the PLL is modulating or not can be programmed by writing to the PLL registers through the
bus interface.
7.1.3.2
Normal PLL Mode with External Reference
Same as
Section 7.1.3.1, “Normal PLL Mode with Crystal Reference”
except EXTAL is driven by an
external clock generator rather than a crystal oscillator. However, the input frequency range is the same as
the crystal reference. To enter normal mode with external clock generator reference, the PLL configuration
must be set at reset by overriding the default reset configuration. See
Chapter 9, “Chip Configuration
for details on setting the device for external reference.
7.1.3.3
Input Clock (Limp) Mode
Through the use of RCON, the device may be booted into a low-frequency limp mode, in which the PLL
is bypassed and the device runs from a factor of the input clock (EXTAL). In this mode, EXTAL feeds a
5-bit programmable counter that divides the input clock by 2
n
, where
n
is the value of the programmable
counter field, MISCCR[LPDIV]. For more information on programming the divider, see
The programmed value of the divider may be changed without glitches or
otherwise negative affects to the system.
While in this mode, the PLL is placed in bypass mode to reduce overall system power consumption. A 3:1
ratio is maintained between the core and the primary bus clock. Because they do not function at speeds as
low as the minimum input clock frequency, the SDRAM controller and FEC are not functional in limp
mode.
When switching from LIMP mode to normal functional mode, you must ensure that any peripheral
transactions in progress (e.g. Ethernet frame reception/transmission or LCD refresh) are allowed to
complete to avoid data loss or corruption.
Limp mode may also be entered and exited from by writing to the MISCCR[LIMP] bit. This is useful
because it places the PLL in a state where the multiplication factor (PFMDR) can be altered. Entering limp
mode also requires a special procedure with the SDRAM module. As noted above the SDRAM controller
is disabled in limp mode, so two critical steps must be followed before setting the MISCCR[LIMP] bit.
1. Code execution must be transferred to another memory resource. Primary options are whatever
memory device is attached to the FlexBus boot chip select or on-chip SRAM (but not the CPU
cache, as it may have to be flushed upon limp mode entrance or exit).
MCF5329 Reference Manual, Rev 3
Содержание MCF5329
Страница 106: ...ColdFire Core 3 32 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 126: ...Enhanced Multiply Accumulate Unit EMAC 4 20 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 148: ...Cache 5 22 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 154: ...Static RAM SRAM 6 6 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 184: ...Power Management 8 18 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 204: ...Reset Controller Module 10 8 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 220: ...System Control Module SCM 11 16 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 228: ...Crossbar Switch XBS 12 8 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 268: ...General Purpose I O Module 13 40 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 392: ...SDRAM Controller SDRAMC 18 30 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 436: ...Fast Ethernet Controller FEC 19 44 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 564: ...Liquid Crystal Display Controller LCDC 22 44 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 594: ...FlexCAN 23 30 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 678: ...Pulse Width Modulation PWM Module 26 22 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 684: ...Watchdog Timer Module 27 6 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 692: ...Programmable Interrupt Timers PIT0 PIT3 28 8 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 704: ...DMA Timers DTIM0 DTIM3 29 12 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 720: ...Queued Serial Peripheral Interface QSPI 30 16 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 754: ...UART Modules 31 34 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 770: ...I2 C Interface 32 16 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 790: ...Message Digest Hardware Accelerator MDHA 33 20 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 866: ...Debug Module 36 50 Freescale Semiconductor MCF5329 Reference Manual Rev 3...
Страница 902: ...Register Memory Map Quick Reference A 26 Freescale Semiconductor MCF5329 Reference Manual Rev 3...