PXD10RM Datasheet, PDF (205/1332 Pages) Freescale Semiconductor, Inc – PXD10 Microcontroller

8.6 32 kHz OSC digital interface
8.6.1 Introduction
The OSC Digital Interface controls the external crystal oscillator (SXOSC). It holds control and status
registers accessible for application.
8.6.2 Main features
• External crystal oscillator (SXOSC) digital interface
• Oscillator powerdown control and status
• Oscillator clock available interrupt
• Oscillator bypass mode
• Output clock division factors ranging from 1,2,3....32
8.6.3 Functional description
The crystal oscillator circuit includes an internal oscillator driver and an external crystal circuitry. It can
be used as a reference clock to specific modules depending on system needs.
The crystal oscillator is controlled by the OSC_CTL register. The OSCON bit controls the powerdown
while S_OSC bit provides the oscillator clock available status.
After system reset, the oscillator is put to power down state and software has to switch on when required.
Whenever the crystal oscillator is switched on from off state, OSCCNT counter starts and when it reaches
the value EOCV[7:0]*512, oscillator clock is made available to the system. Also an interrupt pending bit
I_OSC of OSC_CTL register is set. An interrupt will be generated if the interrupt mask bit M_OSC is set.
The oscillator circuit can be bypassed by writing OSCBYP bit to OSC_CTL register to ‘1’. This bit can
only be set by the software. System reset is needed to reset this bit. In this bypass mode, the output clock
has the same polarity as external clock applied on EXTAL32 pin and the oscillator status is forced to ‘1’.
The bypass configuration is independent of the powerdown mode of the oscillator.
The table below shows the truth table of different configurations of oscillator.
Table 8-16. Truth table of crystal oscillator
OSCON
0
x
1
OSCBYP
0
1
0
XTAL32 EXTAL32 CK_OSCM
OSC MODE
No crystal,
High Z
Ext clock
Crystal
Gnd
No crystal,
High Z
x
Crystal
Ext clock
0
EXTAL32
EXTAL32
EXTAL32
Power down, IDDQ
Bypass, OSC Disabled
Normal, OSC Enabled
Normal, OSC Enabled
Freescale Semiconductor
PXD10 Microcontroller Reference Manual, Rev. 1
Preliminary—Subject to Change Without Notice
8-27