SX18AC/SO Parallax Inc, SX18AC/SO Datasheet - Page 21

• Manufacturer Part Number: SX18AC/SO
• Description: IC MCU 2K FLASH 50MHZ SO-18
• Manufacturer: Parallax Inc
• Series: SXr

Specifications of SX18AC/SO

• Core Processor: RISC
• Core Size: 8-Bit
• Speed: 50MHz
• Number Of I /o: 12
• Program Memory Size: 3KB (2K x 12)
• Program Memory Type: FLASH
• Ram Size: 137 x 8
• Oscillator Type: Internal
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 18-SOIC
• Voltage - Supply (vcc/vdd): -
• Eeprom Size: -
• Data Converters: -
• Peripherals: -
• Connectivity: -

Note:Resistor R
(both crystal and resonator circuits.)
9.2 External RC Mode
The external RC oscillator mode provides a cost-effective
approach for applications that do not require a precise
operating frequency. In this mode, the RC oscillator fre-
quency is a function of the supply voltage, the resistor (R)
and capacitor (C) values, and the operating temperature.
In addition, the oscillator frequency will vary from unit to
unit due to normal manufacturing process variations. Fur-
thermore, the difference in lead frame capacitance
between package types also affects the oscillation fre-
quency, especially for low C values. The external R and
C component tolerances contribute to oscillator fre-
quency variation as well.
Figure 9-3 shows the external RC connection diagram.
The recommended R value is from 3k
values below 2.2k , the oscillator may become unstable,
or may stop completely. For very high R values (such as
1 M ), the oscillator becomes sensitive to noise, humid-
ity, and leakage.
Although the oscillator will operate with no external
capacitor (C = 0pF), it is recommended that you use val-
ues above 20 pF for noise immunity and stability. With no
or small external capacitance, the oscillation frequency
can vary significantly due to variation in PCB trace or
package lead frame capacitances.
In the external RC mode, the OSC2/CLKOUT pin pro-
vides an output frequency, which the input frequency
divided by four.
© 1998 Scenix Semiconductor, Inc. All rights reserved.
Type
Osc
HS
HS
HS
HS
HS
HS
HS
HS
HS
XT
Table 9-2. Component Selection for
Resonator
Frequency
f
is not required for the Version 2.1 device
Crystal Oscillator
12
16
20
25
30
36
40
50
4
8
(pF)
C1
20
20
20
15
15
5
5
5
5
5
to 100k . For R
(pF)
C2
47
47
47
30
30
20
20
15
15
10
4.7k
3.3k
3.3k
3.3k
10k
1M
1M
1M
1M
1M
RF
- 21 -
9.3 Internal RC Mode
The internal RC mode uses an internal oscillator, so the
device does not need any external components. At 4
MHz, the internal oscillator provides +/–8% accuracy
over the allowed temperature range. The internal clock
frequency can be divided down to provide one of eight
lower-frequency choices by selecting the desired value in
the FUSE Word register. The frequency range is from
31.25 KHz to 4 MHz.
V
dd
Figure 9-3. RC Oscillator Mode
R
OSC1
N
C
SX Device
SX18AC / SX20AC / SX28AC
~ ~
Internal
Circuitry
4
OSC2
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