5.0 Functional Description (Continued)
5.10 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 1
.
TABLE 1. 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
5.10.1 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 2
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 2. Crystal Oscillator Configuration,
T
A
= 25˚C, V
CC
=5V
R1 (kΩ)R2(MΩ) C1 (pF) C2 (pF)
CKI Freq.
(MHz)
0 1 18 18 15
0 1 20 20 10
0 1 25 25 4
5.6 1 100 100–156 0.455
5.10.2 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.
5.10.3 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 5 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 3
shows the oscillator frequency
as a function of external capacitance on the CKI pin.
Figure
14
shows the R/C oscillator configuration.
TABLE 3. R/C Oscillator Configuration,
−40˚C to +85˚C, V
CC
= 4.5V to 5.5V,
OSC Freq. Variation of
±
35%
External
Capacitor (pF)*
R/C OSC Freq
(MHz)
Instr. Cycle (µs)
0 5 2.0
9 4 2.5
52 2 5.0
125 1 10
6100 32 kHz 312.5
* Assumes 3-5 pF board capacitance.
With On-Chip Bias Resistor Without On-Chip Bias Resistor
10131717 10131718
FIGURE 12. Crystal Oscillator
COP8SG Family
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