COP8SAC7SLB8 datasheet(18/60 Pages) NSC

18 / 60 page

6.0 Functional Description (Continued)

The contents of data registers and RAM are unknown fol-

lowing the on-chip reset.

6.8 OSCILLATOR CIRCUITS

There are four clock oscillator options available: Crystal

Oscillator with or without on-chip bias resistor, R/C Oscillator

with on-chip resistor and capacitor, and External Oscillator.

The oscillator feature is selected by programming the ECON

Table 2.

TABLE 2. Oscillator Option

ECON4

ECON3

Oscillator Option

External Oscillator

Crystal Oscillator without Bias Resistor

R/C Oscillator

Crystal Oscillator with Bias Resistor

6.8.1 Crystal Oscillator

The crystal Oscillator mode can be selected by programming

ECON Bit 4 to 1. CKI is the clock input while G7/CKO is the

clock generator output to the crystal. An on-chip bias resistor

connected between CKI and CKO can be enabled by pro-

gramming ECON Bit 3 to 1 with the crystal oscillator option

selection. The value of the resistor is in the range of 0.5M to

2M (typically 1.0M).

Table 3 shows the component values

required for various standard crystal values. Resistor R2 is

only used when the on-chip bias resistor is disabled.

Figure

12 shows the crystal oscillator connection diagram.

TABLE 3. Crystal Oscillator Configuration,

A = 25˚C, VCC =5V

R1 (k

Ω)R2 (MΩ) C1 (pF) C2 (pF)

CKI Freq. (MHz)

30–36

5.6

100

100–156

0.455

6.8.2 External Oscillator

The External Oscillator mode can be selected by program-

ming ECON Bit 3 to 0 and ECON Bit 4 to 0. CKI can be

driven by an external clock signal provided it meets the

specified duty cycle, rise and fall times, and input levels.

G7/CKO is available as a general purpose input G7 and/or

Halt control.

Figure 13 shows the external oscillator connec-

tion diagram.

6.8.3 R/C Oscillator

The R/C Oscillator mode can be selected by programming

ECON Bit 3 to 1 and ECON Bit 4 to 0. In R/C oscillation

mode, CKI is left floating, while G7/CKO is available as a

general purpose input G7 and/or HALT control. The R/C

controlled oscillator has on-chip resistor and capacitor for

maximum R/C oscillator frequency operation. The maximum

frequency is 6 MHz ± 35% for V

CC between 4.5V to 5.5V

and temperature range of −40˚C to +85˚C. For max fre-

quency operation, the CKI pin should be left floating. For

lower frequencies, an external capacitor should be con-

nected between CKI and either V

CC or GND. Immunity of the

R/C oscillator to external noise can be improved by connect-

ing one half the external capacitance to V

CC and one half to

GND. PC board trace length on the CKI pin should be kept

as short as possible.

Table 4 shows the oscillator frequency

as a function of approximate external capacitance on the

CKI pin.

Figure 14 shows the R/C oscillator configuration.

TABLE 4. R/C Oscillator Configuration,

−40˚C to +85˚C, V

CC = 4.5V to 5.5V,

OSC Freq. Variation of ± 35%

External Capacitor

R/C OSC Freq

Instr. Cycle

(pF)

(MHz)

(µs)

1.667

2.5

5.0

120

5600

32 kHz

312.5

DS012838-15

FIGURE 10. Reset Timing (Power-On Reset Enabled)

with V

CC Tied to RESET

DS012838-16

FIGURE 11. Reset Circuit Using Power-On Reset

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