HD6473847RHV Datasheet, PDF (140/546 Pages) Renesas Technology Corp – Renesas 8-Bit Single-Chip Microcomputer H8 Family / H8/300L Super Low Power Series

Section 4 Clock Pulse Generators
Oscillation stabilization standby time = oscillation stabilization time + standby time
= trc + (8 to 16,384 states) *¹................. (1)
(to 131,072 states) *²
Notes: 1. H8/3802 Group, H8/38004 and H8/38002S Group
2. H8/38104 Group
Therefore, when a transition is made from standby mode, watch mode, or subactive mode, to
active (high-speed/medium-speed) mode, with a resonator connected to the system clock
oscillator, careful evaluation must be carried out on the installation circuit before deciding on the
oscillation stabilization standby time. In particular, since the oscillation settling time is affected by
installation circuit constants, stray capacitance, and so forth, suitable constants should be
determined in consultation with the resonator manufacturer.
4.6.4 Notes on Use of Resonator
When a microcomputer operates, the internal power supply potential fluctuates slightly in
synchronization with the system clock. Depending on the individual resonator characteristics, the
oscillation waveform amplitude may not be sufficiently large immediately after the oscillation
stabilization standby time, making the oscillation waveform susceptible to influence by
fluctuations in the power supply potential. In this state, the oscillation waveform may be disrupted,
leading to an unstable system clock and erroneous operation of the microcomputer.
If erroneous operation occurs, change the setting of standby timer select bits 2 to 0 (STS2 to
STS0) (bits 6 to 4 in system control register 1 (SYSCR1)) to give a longer standby time.
For example, if erroneous operation occurs with a standby time setting of 16 states, check the
operation with a standby time setting of 1,024* states or more.
If the same kind of erroneous operation occurs after a reset as after a state transition, hold the RES
pin low for a longer period.
Note: * This figure applies to the H8/3802, H8/38004 and H8/38002S Groups. The number of
states on the H8/38104 Group is 8,192 or more.
Rev. 7.00 Mar. 08, 2010 Page 108 of 510
REJ09B0024-0700