SH7058 Datasheet, PDF (120/1130 Pages) Renesas Technology Corp – Renesas SuperHTM RISC engine

5.4 Oscillation Stop Detection Function
5.4.1 Overview
The oscillation stop detection circuit detects errors in the crystal oscillator and sets flags in internal
peripheral registers. To make this function effective, the INOSCE bit in SYSCR1 needs to be set
to 1 (initial value: 0). If the crystal oscillator performs abnormal operation, such as oscillation
stop, for some reason or other, the OSCSTOP bit in SYSCR1 is set to 1 (initial value: 0). In
addition, the LSI shuts off clocks from the crystal oscillator and continues to operate by using
clocks from the on-chip oscillator circuit. If abnormal operation of the crystal oscillator is detected
once, the status is retained until the next reset is released or software standby is released. When
this function of oscillation stop detection is made ineffective (the INOSCE bit in SYSCR1 is set to
0), abnormal operations of the crystal oscillator are not detected. Switchover to on-chip oscillation
does not take place, either.
5.4.2 Settings of Oscillation Stop Detection Function
To make the oscillation stop detection function effective, the INOSCE bit in SYSCR1 needs to be
set to 1 (initial value: 0). The INOSCE bit in SYSCR1 is always cleared to 0 after reset or
software standby is released. To make this function effective, make sure to set the INOSCE bit to
1 after reset or software standby is released.
While the oscillation stop detection function is made effective, if the clocks from the crystal
oscillator are not supplied for a certain period (see table 5.6), the status is determined as abnormal
operation of the crystal oscillator and the LSI starts to use the clocks from the on-chip oscillator
circuit (see table 5.7). In this case, the LSI sets the OSCSTOP bit in SYSCR1 to 1 (initial value:
0). Once switchover to on-chip oscillation takes place, operation by on-chip oscillation continues
even if the crystal oscillator performs normally afterwards. To use the clocks from the crystal
oscillator, perform reset start again.
Rev. 3.0, 09/04, page 79 of 1086