EM78P258N
8-Bit Microprocessor with OTP ROM
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 and cannot and should not be defined as normal I/O pins.
NOTE
The transient point of system frequency between HXT and LXY is around 400 KHz.
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
6.10.2 Crystal Oscillator/Ceramic Resonators (XTAL)
EM78P258N can be driven by an external clock signal through the OSCI pin as
illustrated below.
OSCI
EM78P258N
OSCO
Fig. 6-13 External Clock Input Circuit
56 •
Product Specification (V1.0) 06.16.2005
(This specification is subject to change without further notice)
ELAN [ ELAN MICROELECTRONICS CORP ]
