EM78P341N/342N/343N
8-Bit Microprocessor with OTP ROM
Circuit diagrams for serial and parallel modes Crystal/Resonator:
330
330
C
OSCI
7404
7404
7404
Crystal
Fig. 6-19 Serial Mode Crystal/Resonator Circuit Diagram
4.7K
10K
7404
Vdd
OSCI
7404
10K
Crystal
10K
C1
C2
Fig. 6-20 Parallel Mode Crystal/Resonator Circuit Diagram
6.11.3 External RC Oscillator Mode
For some applications that do not require
precise timing calculation, the RC
Vcc
Rext
oscillator (Fig. 6-21 at right) offers a cost-
effective solution. Nevertheless, it should
be noted that the frequency of the RC
oscillator is influenced by the supply
voltage, the values of the resistor (Rext),
the capacitor (Cext), and even by the
operation temperature. Moreover, the
frequency also changes slightly from one
chip to another due to manufacturing
process variations.
OSCI
Cext
Fig. 6-21 External RC Oscillator Mode Circuit
In order to maintain a stable system frequency, the values of the Cext should be no less
than 20pF, and that of Rext should be no greater than 1MΩ. If the frequency cannot be
kept within this range, the frequency can be affected easily by noise, humidity, and
leakage.
The smaller the Rext in the RC oscillator is, the faster its frequency will be. On the
contrary, for very low Rext values, for instance, 1 KΩ, the oscillator will become
unstable because the NMOS cannot correctly discharge the capacitance current.
Product Specification (V1.0) 12.01.2006
(This specification is subject to change without further notice)
• 71
ELAN [ ELAN MICROELECTRONICS CORP ]
