EM78156E
8-Bit Microcontroller with MASK ROM
4.8 CODE Option Register
The EM78156E has a CODE option word that is not a part of the normal program
memory. The option bits cannot be accessed during normal program execution.
Bit0
Bit1
Bit2
Bit3
Bit4
Bit5
LVDD
CLK
/ENWDT
HLF
MS
-
Bit 0 (LVDD):
Bit 1 (CLK):
Levels of the Operating Voltage.
0: Operating Voltage 2.3V ~ 5.5V, non-power saving.
1: Operating Voltage 4V ~ 5.5V, power saving.
Instruction period option bit.
0: two oscillator periods.
1: four oscillator periods.
Refer to the section on Instruction Set.
Bit 2 (/ENWDT): Watchdog timer enable bit.
0: Enable
1: Disable
Bit 3 (HLF):
XTAL frequency selection
0: XTAL2 type (low frequency, 32.768KHz)
1: XTAL1 type (high frequency)
This bit will affect system oscillation only when Bit4(MS) is “1”. When MS is”0”, HLF
must be “0”.
NOTE
The transient point of system frequency between HXT and LXY is around 400 KHz.
Bit 4 (MS):
Oscillator type selection.
0: RC type
1: XTAL type (XTAL1 and XTAL2)
Reserved.
Bit 5:
The bit is set to “1” all the time.
4.9 Power On Considerations
Any microcontroller is not guaranteed to start to operate properly before the power
supply stays at its steady state.
EM78156E POR voltage range is 1.2V~1.8V. Under customer application, when
power is OFF, Vdd must drop to below 1.2V and remains OFF for 10us before power
can be switched ON again. This way, the EM78156E will reset and work normally. The
Product Specification (V1.3) 07.29.2004
• 25
(This specification is subject to change without further notice)
ELAN [ ELAN MICROELECTRONICS CORP ]
