EM78156E
8-Bit Microcontroller with MASK ROM
4.7 Oscillator
4.7.1 Oscillator Modes
The EM78156E can be operated in three different oscillator modes, such as External
RC oscillator mode (ERC), High XTAL oscillator mode(HXT), and Low XTAL oscillator
mode(LXT). User can select one of them by programming MS and HLF in the CODE
option register. Table 8 depicts how these three modes are defined.
The up-most limited operation frequency of crystal/resonator on the different VDDs is
listed in Table 9.
Table 8 Oscillator Modes Defined by MS and HLP
Mode
MS
0
HLF
ERC(External RC oscillator mode)
HXT(High XTAL oscillator mode)
LXT(Low XTAL oscillator mode)
*X
1
1
1
0
NOTE
1. X, Don’t care
2. The transient point of system frequency between HXT and LXY is around 400 KHz.
Table 9 The Summary of Maximum Operating Speeds
Conditions
VDD
2.3
Fxt max.(MHz)
4.0
8.0
Two cycles with two clocks
3.0
5.0
20.0
4.7.2 .Crystal Oscillator/Ceramic Resonators(XTAL)
EM78156E can be driven by an external clock signal through the OSCI pin as shown in
Fig. 11 below.
OSCI
OSCO
Ext. Clock
EM78156E
Fig. 11 Circuit for External Clock Input
22 •
Product Specification (V1.3) 07.29.2004
(This specification is subject to change without further notice)
ELAN [ ELAN MICROELECTRONICS CORP ]
