em78p257 ELAN Microelectronics Corp, em78p257 Datasheet - Page 66

• Manufacturer Part Number: em78p257
• Description: 8-bit Microcontroller
• Manufacturer: ELAN Microelectronics Corp

This specification is subject to change without prior notice.
• Bit 10 (CLKS): Instruction period option bit.
• Bit 9, 8 and 7 (OSC2,OSC1 and OSC0): Oscillator Modes Selection bits.
• Bit 6 (/PTB): Protect bit.
• Bit 5 (SUT): Set-Up Time of device bits.
*Theoretical values, for reference only
• Bit 4 (TYP): Type selection for EM78P257A or EM78P257B.
• Bit 3 (RCOUT): A selecting bit of Oscillator Output or I/O port for RC Oscillator.
• Bit 2, and Bit 1 ( RCM1, RCM0): IRC mode selection bits
• Bit0 : Not used
<Note>
Table 32 Oscillator Modes Defined by OSC2,OSC1 and OSC0
<Note> *Theoretical values, for reference only. In fact, the values may be inaccurate by 35%.
IRC(Internal RC oscillator mode)
IC(Internal C oscillator mode)
ERC(External RC oscillator mode)
HXT(High XTAL oscillator mode)
LXT(Low XTAL oscillator mode)
0: Enable
1: Disable
0: Two clocks
1: Four clocks
Refer to the section on Instruction Set.
0: Enable
1: Disable
RCOUT
TYPE
SUT
RCM 1
1
0
0
1
0
1
1
1
0
0
The transient point of system frequency between HXT and LXY is around 400 KHz.
Mode
RCM 0
1
0
1
0
*Set-Up Time
EM78P257B
EM78P257A
Pin Function
Series
OSCO
18 ms
1 ms
P70
OSC2
66
1
1
1
0
0
*Frequency(MHz)
32.768kHz
455kHz
OSC1
4
1
1
1
0
0
0
OSC0
1
0
1
1
0
EM78P257
07.27.2004 (V1.4)
OTP ROM