Datasheet

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
register, which is summarized in
Table 2 .
TABLE 2. Oscillator Option
ECON4 ECON3 Oscillator Option
0 0 External Oscillator
1 0 Crystal Oscillator without Bias Resistor
0 1 R/C Oscillator
1 1 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,
T
A
= 25˚C, V
CC
=5V
R1 (kΩ)R2(MΩ) C1 (pF) C2 (pF) CKI Freq. (MHz)
0 1 30 30 15
0 1 32 32 10
0 1 45 30–36 4
5.6 1 100 100–156 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)
0 6 1.667
13 4 2.5
62 2 5.0
120 1 10
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
COP8SA Family
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