SH7144 Datasheet, PDF (90/773 Pages) Renesas Technology Corp – Hitachi SuperH RISC engine

EXTAL
XTAL
External clock input
Open state
Figure 4.4 Example of External Clock Connection
4.2 Function for Detecting the Oscillator Halt
This CPG can detect a clock halt and automatically cause the timer pins to become high-
impedance when any system abnormality causes the oscillator to halt. That is, when a change of
EXTAL has not been detected, the high-current 6 pins (PE9/TIOC3B/SCK3/TRST*,
PE11/TIOC3D/RXD3/TDO*, PE12/TIOC4A/TXD3/TCK*, PE13/TIOC4B/MRES,
PE14/TIOC4C/DACK0, PE15/TIOC4D/DACK1/IRQOUT) can be set to high-impedance
regardless of PFC setting. Refer to section 17.1.11, High-Current Port Control Register (PPCR),
for more details.
Even in software standby mode, these 6 pins can be set to high-impedance regardless of PFC
setting. Refer to section 17.1.11, High-Current Port Control Register (PPCR), for more details.
These pins enter the normal state after software standby mode is released. When abnormalities that
halt the oscillator occur except in software standby mode, other LSI operations become undefined.
In this case, LSI operations, including these 6 pins, become undefined even when the oscillator
operation starts again.
In the case of using E10A, the high-impedance function is disabled when an oscillation stop is
detected, or when in software standby state for the three pins of PE9/TIOC3B/SCK3/TRST,
PE11/TIOC3D/RXD3/TDO, and PE12/TIOC4A/TxD3/TCK of the SH7145.
Note: * Only in the SH7145.
4.3 Usage Notes
4.3.1 Note on Crystal Resonator
A sufficient evaluation at the user’s site is necessary to use the LSI, by referring the resonator
connection examples shown in this section, because various characteristics related to the crystal
resonator are closely linked to the user’s board design. As the oscillator circuit's circuit constant
will depend on the resonator and the floating capacitance of the mounting circuit, the value of each
external circuit’s component should be determined in consultation with the resonator
manufacturer. The design must ensure that a voltage exceeding the maximum rating is not applied
to the oscillator pin.
Rev. 2.0, 09/02, page 50 of 732