NXP Semiconductors MPC5606S - Khz OSC Digital Interface

Clock Description
MPC5606S Microcontroller Reference Manual, Rev. 7
Freescale Semiconductor 211
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 that are accessible by software.
8.6.2 Main features
• External crystal oscillator (SXOSC) digital interface
• Oscillator power-down 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 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 power-down
while the S_OSC bit provides the oscillator clock available status.
After system reset, the oscillator is put into power-down state and software has to start it up when required.
Whenever the crystal oscillator is switched on from an off state, the OSCCNT counter starts. When it
reaches the value of EOCV[7:0] × 512, the oscillator clock is made available to the system. Also, an
interrupt pending bit, I_OSC of the OSC_CTL register, is set. An interrupt is generated if the interrupt
mask bit M_OSC is set.
The oscillator circuit can be bypassed by setting the OSCBYP bit in the 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 power-down mode of the oscillator.
The table below shows the truth table of different configurations of the oscillator.
Table 8-16. Truth table of crystal oscillator
OSCON OSCBYP XTAL32 EXTAL32 CK_OSCM OSC MODE
0 0 No crystal,
high Z
No crystal,
high Z
0 Power down, IDDQ
x 1 Ext clock x EXTAL32 Bypass, OSC disabled
1 0 Crystal Crystal EXTAL32 Normal, OSC enabled
Gnd Ext clock EXTAL32 Normal, OSC enabled