Mitsubishi DS907x SIP CPU Timing Oscillator, Crystal Connection ±1, Clock Source Input ±2, XTAL1

USER'S GUIDE

SECTION 15: CPU TIMING

OSCILLATOR

The Secure Microcontroller provides an on±chip oscilla- tor circuit which may be driven either by using an exter- nal crystal as a time base or from a TTL±compatible clock signal. The oscillator circuitry provides the internal clocking signals to the on±chip CPU and I/O circuitry.

The schematic shown in Figure 15±1 illustrates the re- quired connections when using a crystal. Typically, the values of C1 and C2 should both be 33 pF. If a resonator is used, C1 and C2 should be 47 pF.

XTAL1

Input to the inverting oscillator amplifier and input to the internal clock generating circuits.

XTAL2

Output from the inverting oscillator amplifier. This pin is also used to distribute the clock to other devices.

Oscillator Characteristics

XTAL1 and XTAL2 are the input and output, respective- ly, of an inverting amplifier which can be configured for use as an on±chip oscillator as shown in Figure 15±1. The crystal should be parallel resonant, AT cut type.

To drive the device from an external clock source, XTAL1 should be driven, while XTAL2 is left uncon- nected as shown in Figure 15±2. There are no require- ments on the duty cycle of the external clock signal since the input to the internal clocking circuitry is through a divide±by±two flip±flop. However, minimum and maximum high and low times specified in the elec- trical specifications must be met to insure proper opera- tion.

CRYSTAL CONNECTION Figure 15±1

Soft Micro

XTAL1	XTAL2
33 pF	33 pF

CLOCK SOURCE INPUT Figure 15±2

NC

EXT. OSC.

SIGNAL

XTAL2

XTAL1

GND

050396 123/173

124