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User’s Manual U11969EJ3V0UM00
139
CHAPTER 6 CLOCK GENERATOR FUNCTION
6.4 PLL Lock-up
Following the power-on reset or when existing the software STOP mode is released, a certain length of time will
be required for the PLL to stabilize. This required time is called PLL lock-up time. The status in which the frequency
is not stable is called unlock status and the status in which it has been stabilized is called lock status.
Two system status registers are available to check the stabilization of the PLL frequency: UNLOCK flag that
indicates the stabilization status of the PLL frequency, and PRERR flag that indicates occurrence of a protection error
(for the details of the PRERR flag, refer to 3.4.9 (2) System status register (SYS)).
The SYS register, which contains these UNLOCK and PREERR flags, can be read/written in 8- or 1-bit units.
Bit Position
Bit Name
Function
0
UNLOCK
Unlock Status Flag
This is a read-only flag and indicates unlock status of PLL.
It holds “0” as long as lock up status is maintained, and is not changed even if system is
reset.
0 : Indicates lock status
1 : Indicates unlock status
Remark
For the description of the PRERR flag, refer to 3.4.9 (2) System status register (SYS).
If the unlock status condition should arise, due to a power or clock source failure, the UNLOCK flag should be
checked to verify that the PLL has stabilized before performing any execution speed dependent operations, such as
real-time processing.
Static processing such as setting of the on-chip hardware units and initialization of the register data and memory
data, however, can be executed before the UNLOCK flag is reset.
The following is the relation between the oscillation stabilization time (the time from the oscillator starts oscillating
until the input wave form stabilizes) and the PLL lockup time (the time until the frequency stabilizes) when using an
oscillator:
Oscillation stabilization time < PLL lockup time
Address
FFFFF078H
7
0
SYS
6
0
5
0
4
PRERR
3
0
2
0
1
0
0
UNLOCK
After reset
0000000xB
Содержание V854 UPD703006
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