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¡ Semiconductor

MSM82C84A-2RS/GS/JS

OPERATIONAL DESCRIPTION

(1) Oscillator Circuit

The MSM82C84A-2 internal oscillator circuit can be driven by connecting a crystal oscillator to

The frequency of the crystal oscillator in this case needs to be three times greater than the desired

CLK frequency.

Since the oscillator circuit output (the same output as for the crystal resonator frequency)

appears at the OSC pin, independent use of this output is also possible.

Oscillator Circuit Example





MSM

82C84A-2

OSC

Crystal Oscillator

When input frequency is 6 to 15 MHz

When input frequency is 15 to 24 MHz

Note: Because Oscillator circuit and values depend on crystal oscillator characteristics,

OKI recommends to make contact with crystal oscillator vendor to determine

the best circuit and values for customers' application.

(2) Clock Generator Circuit

This circuit generates two clock outputs-CLK obtained by dividing the input external clock or

crystal oscillator circuit output by three, and PCLK obtained by halving CLK. CLK and PCLK

are generated from the external clock applied to the EFI pin when F/C is at high level, and are

generated from the crystal oscillator circuit when at low level.

(3) Reset Circuit

Since a Schmitt trigger circuit is used in the RES input, the MSM82C84A-2 can be reset by “power

on” by connection to a simple RC circuit. If the MSM80C86A-10 or MSM80C88A-10 is used as

the CPU in this case, it is necessary to keep the RES input at low level for at least 50 ms after Vcc

reaches the 4.5V level.