UPD784938 Datasheet, PDF (641/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 25 STANDBY FUNCTION
25.2.2 Oscillation stabilization time specification register (OSTS)
OSTS specifies the oscillator operation and the oscillation stabilization time when STOP mode is released. The EXTC
bit of OSTS specifies whether crystal/ceramic oscillation or an external clock is used. STOP mode can be set when external
clock input is used only when the EXTC bit is set (to 1).
Bits OSTS0 to OSTS2 of OSTS select the oscillation stabilization time when STOP mode is released. In general, an
oscillation stabilization time of at least 40 ms should be selected when a crystal resonator is used, and at least 4 ms when
a ceramic oscillator is used.
The time taken for oscillation stabilization is affected by the crystal resonator or ceramic resonator used, and the
capacitance of the connected capacitor. Therefore, if you want to set a short oscillation stabilization time, you should consult
the crystal resonator or ceramic resonator manufacturer.
OSTS can be written to only with an 8-bit transfer instruction.
RESET input clears OSTS to 00H.
The format of OSTS is shown in Figure 25-4.
Figure 25-4. Oscillation Stabilization Time Specification Register (OSTS) Format
7
6
5
4
3
2
1
0 Address After reset R/W
OSTS 0
0
0
0
0 OSTS2 OSTS1 OSTS0 0FFCFH 00H R/W
OSTS2 OSTS1 OSTS0
(fXX = 12.58 MHz)
Oscillation Stabilization
Time Selection Bits
0
0
0 2¹⁹/fXX (41.7 ms)
0
0
1 2¹⁸/fXX (20.8 ms)
0
1
0 2¹⁷/fXX (10.4 ms)
0
1
1 2¹⁶/fXX (5.2 ms)
1
0
0 2¹⁵/fXX (2.6 ms)
1
0
1 2¹⁴/fXX (1.3 ms)
1
1
0 2¹³/fXX (0.7 ms)
1
1
1 Setting prohibited
Caution When using the regulator (Refer to CHAPTER 5 REGULATOR), set a value of at least 10.4 ms, taking
in consideration the regulator output stabilization time.
Preliminary User’s Manual U13987EJ1V0UM00
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