XC886/888CLM
Power Supply, Reset and Clock Management
User’s Manual
7-12
V1.3, 2010-02
Power, Reset and Clock, V 1.0
7.3.1.1
Functional Description
When the XC886/888 is powered up, the PLL is disconnected from the oscillator and will
run at its VCO base frequency. After the EVR is stable, provided the oscillator is running,
the PLL will be connected and the continuous lock detection will ensure that the PLL
starts functioning. Once reset has been released, bit OSCR will be set to 1 if the oscillator
is running and bit LOCK will be set to 1 if the PLL is locked.
Loss-of-Lock Operation
If the PLL is not the system’s clock source (VCOBYP = 1) when the loss of lock is
detected, only the lock flag is reset (PLL_CON.LOCK = 0) and no further action is taken.
This allows the PLL parameters to be switched dynamically.
If PLL loses its lock to the oscillator, the PLL Loss-of-Lock NMI flag NMISR.FNMIPLL is
set and an NMI request to the CPU is activated if PLL NMI is enabled
(NMICON.NMIPLL). In addition, the LOCK flag in PLL_CON is reset. The oscillator must
be disconnected immediately via the NMI routine upon PLL Loss-of-Lock to force PLL to
run in VCO base frequency. Emergency routines can be executed with the XC886/888
clocked with this base frequency.
The XC886/888 remains in this loss-of-lock state until the next power-on reset, hardware
reset or after a successful lock recovery has been performed.
Note: While PLL is running in VCO base frequency i.e.
f
sys
= f
V
CObase
/K. Read from Flash
is possible at low frequency. However, Flash program or erase operation is not
allowed.
Loss-of-Lock Recovery
If PLL has lost its lock to the oscillator, the PLL can be re-locked by software. The
following sequence must be performed:
1. Select the VCO bypass mode (VCOBYP = 1).
2. Disconnect the oscillator from the PLL (OSCDISC = 1).
3. Wait until the oscillator is stable.
4. Restart the Oscillator Run Detection by setting bit OSC_CON.ORDRES.
5. Wait for 2048 cycles based on VCO frequency.
If bit OSC_CON.OSCR is set, then:
1. Reconnect oscillator to the PLL (OSCDISC = 0).
2. The RESLD bit must be set and the LOCK flag checked. Only if the LOCK flag is set
again can the VCO bypass mode be deselected and normal operation resumed.
If neither OSCR nor LOCK is set, emergency measures must be executed. Emergency
measures such as a system shut down can be carried out by the user.
*
Содержание XC886CLM
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