MC80F0804D View Datasheet(PDF) - Unspecified

Part Name

Description

Manufacturer

MC80F0804D

8-BIT SINGLE-CHIP MICROCONTROLLERS

Unspecified 

MC80F0704/0708/0804/0808

ing capacities.

- Minimize the wiring length.

- Do not allow wiring to intersect with other signal conductors.

- Do not allow wiring to come near changing high current.

- Set the potential of the grounding position of the oscillator capac-

itor to that of VSS. Do not ground to any ground pattern where high

current is present.

- Do not fetch signals from the oscillator.

n addition, see Figure 10-3 for the layout of the crystal.

XOUT

XIN

The user needs to take into account variation due to tolerance of

external R and C components used.

Figure 10-1 shows how the RC combination is connected to the

MC80F0704/0708/0804/0808. External capacitor (CEXT) can be

omitted for more cost saving. However, the characteristics of ex-

ternal R only oscillation are more variable than external RC os-

cillation.

Vdd

REXT

CEXT

fXIN÷4

XIN

Cint ≈ 6pF

XOUT

Figure 10-1 RC Oscillator Connections

Figure 10-3 Layout of Oscillator PCB circuit

To drive the device from an external clock source, Xout should

be left unconnected while Xin is driven as shown in Figure 10-4

. There are no requirements 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, but minimum and maximum high and

low times specified on the data sheet must be observed.

Oscillation circuit is designed to be used either with a ceramic

resonator or crystal oscillator. Since each crystal and ceramic res-

onator have their own characteristics, the user should consult the

crystal manufacturer for appropriate values of external compo-

nents.

OPEN

Xout

External

Clock

Xin

Source

Vss

Figure 10-4 External Clock Connections

In addition, the MC80F0704/0708/0804/0808 has an ability for

the external RC oscillated operation. It offers additional cost sav-

ings for timing insensitive applications. The RC oscillator fre-

quency is a function of the supply voltage, the external resistor

(REXT) and capacitor (CEXT) values, and the operating tempera-

ture.

VDD

REXT

fXIN÷4

XIN

CINT ≈ 6pF

XOUT

Figure 10-2 R Oscillator Connections

To use the RC oscillation, the CLK option of the configuration

bits (20FFH) should be set to “EXRC or EXRCXO”.

The oscillator frequency, divided by 4, is output from the Xout

pin, and can be used for test purpose or to synchronize other logic.

In addition to external crystal/resonator and external RC/R oscil-

lation, the MC80F0704/0708/0804/0808 provides the internal

4MHz or 2MHz oscillation. The internal 4MHz/2MHz oscillation

needs no external parts.

To use the internal 4MHz/2MHz oscillation, the CLK option of

the configuration bits should be set to “IN4MCLK”,

“IN2MCLK”, “IN4MCLKXO” or “IN2MCLKXO”. For detail

description on the configuration bits, refer to "22.. Device Con-

figuration Area" on page 101

44

October 31, 2011 Ver 1.03

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