SH7708 datasheet(181/633 Pages) RENESAS

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Mode 1: An external clock is input from the EXTAL pin and its frequency is multiplied by 4 by

PLL circuit 2 before being supplied inside the SH7708 Series, allowing a low-frequency external

clock to be used. An input clock frequency of 5 MHz to 15 MHz can be used, and the CKIO

frequency range is 20 MHz to 60 MHz.

As PLL circuit 1 compensates for fluctuations in the CKIO pin load, this mode is suitable for

connection of synchronous DRAM.

Mode 2: The on-chip crystal oscillator operates, with the oscillation frequency being multiplied by

4 by PLL circuit 2 before being supplied inside the SH7708 Series, allowing a low crystal

frequency to be used. A crystal oscillation frequency of 5 MHz to 15 MHz can be used, and the

CKIO frequency range is 20 MHz to 60 MHz.

As PLL circuit 1 compensates for fluctuations in the CKIO pin load, this mode is suitable for

connection of synchronous DRAM.

Mode 3: An external clock is input from the EXTAL pin and undergoes waveform shaping by

PLL circuit 2 before being supplied inside the SH7708 Series. PLL circuit 1 is off in the default

state at power-on reset, and PLL circuit 1 can be selected as on or off, enabling power

consumption to be kept lower than in mode 0. An input clock frequency of 8 MHz to 15

MHz(SH7708, SH7708S) or 16 MHz to 25 MHz(SH7708R) can be used, and the CKIO frequency

range is of 8 MHz to 15 MHz(SH7708, SH7708S) or 16 MHz to 25 MHz(SH7708R).

Mode 4: The on-chip crystal oscillator operates, with its output supplied inside the SH7708 Series

as a square waveform by PLL circuit 2. PLL circuit 1 is off in the default state at power-on reset,

and PLL circuit 1 can be selected as on or off, enabling power consumption to be reduced

accordingly. A crystal oscillation frequency of of 8 MHz to 15 MHz(SH7708, SH7708S) or 16

MHz to 25 MHz(SH7708R) can be used, and the CKIO frequency range is of 8 MHz to 15

MHz(SH7708, SH7708S) or 16 MHz to 25 MHz(SH7708R).

Mode 7: In this mode, the CKIO pin is an input, an external clock is input to this pin, and

undergoes waveform shaping, and also frequency multiplication according to the setting, by PLL

circuit 1 before being supplied to the SH7708 Series. In modes 0 to 6, the system clock is

generated from the output of the SH7708 Series’ CKIO pin. Consequently, if a large number of

ICs are operating on the clock cycle, the CKIO pin load will be large. This mode, however,

assumes a comparatively large-scale system. If a large number of ICs are operating on the clock

cycle, a clock generator with a number of low-skew clock outputs can be provided, so that the ICs

can operate synchronously by distributing the clocks to each one.

As PLL circuit 1 compensates for fluctuations in the CKIO pin load, this mode is suitable for

connection of synchronous DRAM.

SH7708 Datasheet(PDF) 181 Page - Renesas Technology Corp