EM78P259N/260N
8-Bit Microprocessor with OTP ROM
6.11 Oscillator
6.11.1 Oscillator Modes
The EM78P259N/260N can be operated in four different oscillator modes, such as High
XTAL oscillator mode (HXT), Low XTAL oscillator mode (LXT), External RC oscillator
mode (ERC), and RC oscillator mode with Internal RC oscillator mode (IRC). You can
select one of them by programming the OSC2, OCS1, and OSC0 in the CODE Option
register.
The Oscillator modes defined by OSC2, OCS1, and OSC0 are described below.
Oscillator Modes
OSC2 OSC1 OSC0
ERC1 (External RC oscillator mode); P70/OSCO acts as P70
ERC1 (External RC oscillator mode); P70/OSCO acts as OSCO
IRC2 (Internal RC oscillator mode); P70/OSCO acts as P70
IRC2 (Internal RC oscillator mode); P70/OSCO acts as OSCO
LXT3 (Low XTAL oscillator mode)
0
0
0
0
1
1
0
0
1
1
1
1
0
1
0
1
0
1
HXT3 High XTAL oscillator mode) (default)
1 Under ERC mode, OSCI is used as oscillator pin. OSCO/P70 is defined by code
option WORD0 Bit6 ~ Bit4.
2 Under IRC mode, P55 is normal I/O pin. OSCO/P70 is defined by code
option WORD0 Bit6 ~ Bit4.
3 Under LXT and HXT modes; OSCI and OSCO are used as oscillator pins. These
pins cannot and should not be defined as normal I/O pins.
NOTE
The transient point of the system frequency between HXT and LXY is around 400kHz.
The maximum operating frequency limit of crystal/resonator at different VDDs, are as
follows:
Conditions
VDD
2.3
Max. Freq. (MHz)
4
8
Two clocks
3.0
5.0
20
Product Specification (V1.0) 06.16.2005
• 61
(This specification is subject to change without further notice)
ELAN [ ELAN MICROELECTRONICS CORP ]
