em78p131a ELAN Microelectronics Corp, em78p131a Datasheet - Page 27

• Manufacturer Part Number: em78p131a
• Description: 8-bit Microcontroller With Otp Rom
• Manufacturer: ELAN Microelectronics Corp

Product Specification (V1.2) 09.16.2009
(This specification is subject to change without further notice)
5.7 Oscillator
5.7.1 Oscillator Modes
The EM78P131A can be operated in four different oscillator modes, such as External
RC oscillator mode (ERC), Internal RC oscillator mode (IRC), High Crystal oscillator
mode (HXT), and Low Crystal oscillator mode (LXT). The desired mode can be
selected by programming OSC1 and OSC2 in the Code Option register. The Table
below describes how these four oscillator modes are defined.
Table 4 Oscillator Modes Defined by OSC
The maximum operational frequency of the crystal/resonator under different VDDs is
as listed below.
Table 5 Summary of Maximum Operating Speeds
5.7.2 Crystal Oscillator/Ceramic Resonators (Crystal)
The EM78P131A can be driven by an external clock signal through the OSCI pin as
shown in the following figure.
Note: The transient point of system frequency between HXT and LXY is 400kHz.
IRC (Internal RC oscillator mode)
ERC (External RC oscillator mode)
HXT (High Crystal oscillator mode)
LXT (Low Crystal oscillator mode)
Two cycles with two clocks
E M 7 8 P 1 3 1 A
Conditions
O S C O
Mode
O S C I
Fig. 5-11 Circuit for External Clock Input
8-Bit Microcontroller with OTP ROM
VDD
2.3
3.0
5.0
OSC1
1
1
0
0
E x t. C lo c k
Max Freq. (MHz)
EM78P131A
20.0
4.0
8.0
OSC2
1
0
1
0
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