NEC V850E/CA1 ATOMIC, Preliminary User'S Manual

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Chapter 8 Clock Generator
Preliminary User’s Manual U14913EE1V0UM00
(1) Start-up after any Power-Save Mode condition recommendation
It is recommended to proceed in the following way when performing power-save functions:
1. Switch off the PLL (PLLEN bit of CKC)
2. Wait for “PLL switch off status” by reading VBSTAT bit in PSTAT register.
3. Enter the desired power-save function
4. (Processor waits on a start-up condition).
5. (Condition fulfilled: Processor wakes up)
6. Let the processor execute at least 5 NOP instructions
7. Let the processor run in a loop that causes a wait for at least 20 Microseconds
8. Switch on the PLL, if desired (PLLEN bit of CKC)
9. Continue with normal operation
8.4.2 PLL Status Register (PSTAT)
This is an 8-bit register that indicates PLL status.
This register can be read in 8- or 1-bit units.
8.4.3 Clock select pin
Two basic operating modes are provided: OSC mode and direct mode. The operating mode is selected
by specifying the CLKSEL pin.
Table 8-1: PLL mode / direct mode
Note: If direct mode is selected by CLKSEL pin = 1, CESEL must be set to 1 by software after reset.
The CLKSEL pin level should be fixed according to the application system. Switching this pin during
operation may cause malfunction.
In OSC mode, the external signal supplied by a connected resonator is used to generate the system
clock that can be multiplied by the PLL synthesizer by setting the PLLEN bit. The input signal from an
external resonator is recommended to range from 4 MHz to 5 MHz, and the PLL synthesizer multiplies
the source clock signal by 4. Therefore, a system clock of up to approximately 20 MHz is available as
shown below, which is suitable for application systems requiring low noise and low power consumption.
7 6 5 4 3 2 1 0 Address R/W At Reset
PSTAT VBSTAT 0 0 0 0 0 0 0 FFFFF824H R xxH
Bit name Function
VBSTAT VBCLOCK status
0: PLL clock is not used for f
CPU
(system clock)
1: PLL clock is used for f
CPU
(system clock)
CLKSEL Description
0 Normal mode using a resonator (crystal
or ceramic)
1
Direct clock input from CLOCKIN
Note