45181 Parallax Inc, 45181 Datasheet - Page 178

• Manufacturer Part Number: 45181
• Description: SX TECH TOOL KIT NO POWER
• Manufacturer: Parallax Inc
• Series: SXr
• Type: Microcontrollerr

Specifications of 45181

• Contents: SX Book, SX Key, SX Tech Board, Samples, Resonators, Cable and Manual
• Product: Microcontroller Basic Stamps
• Operating Supply Voltage: 5 V
• For Use With/related Products: SX MCUs
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

15 Appendix E: SX Data Sheet
15.6.1.2
For timing insensitive applications, the RC device option offers additional cost savings. The RC
oscillator frequency is a function of the supply voltage, the resistor (Rext) and capacitor (Cext) values,
and the operating temperature. In addition to this, the oscillator frequency will vary from unit to unit
due to normal process variation. Furthermore, the difference in lead frame capacitance between
package types will also affect the oscillation frequency, especially for low Cext values. Variation due to
tolerance of external R and C components must also be considered.
Figure 40 - External RC Mode shows the RC connections to the SX. For Rext values below 2.2k , the
oscillator operation may become unstable, or stop completely. For very high Rext values (e.g. 1 M ) the
oscillator becomes sensitive to noise, humidity and leakage. The recommended Rext value is 3k
100k .
Although the oscillator will operate with no external capacitor (Cext = 0 pF), using values above 20 pF is
recommended for noise and stability reasons. With little external capacitance, the oscillation frequency
can vary dramatically due to changes in external capacitance, such as PCB trace capacitance or package
lead frame capacitance.
Page 178 SX-Key/Blitz Development System Manual 2.0 Parallax, Inc.
External RC Mode
Clock signal
from external
system
Figure 39 - SX with External System Clock
Vdd
Figure 40 - External RC Mode
Cext
Rext
Not Connected
OSC1
OSC2
OSC1
OSC2
SX
SX
to