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. Oscillator Option
ECON4
ECON3
Oscillator Option
0
External Oscillator
1
0
Crystal Oscillator without Bias Resistor
0
1
R/C Oscillator
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).
required for various standard crystal values. Resistor R2 is
only used when the on-chip bias resistor is disabled.
12 shows the crystal oscillator connection diagram.
TABLE 2. Crystal Oscillator Configuration,
T
A = 25C, VCC =5V
R1 (k
)R2 (M)
C1 (pF)
C2 (pF)
CKI Freq.
(MHz)
0
1
18
15
0
1
20
10
0
1
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 40C to +85C. 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.
14 shows the R/C oscillator configuration.
TABLE 3. R/C Oscillator Configuration,
40C to +85C, V
CC = 4.5V to 5.5V,
OSC Freq. Variation of ± 35%
External
Capacitor (pF)*
R/C OSC Freq
(MHz)
Instr. Cycle (s)
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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