EM78156EAS datasheet(29/48 Pages) EMC

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EM78156E

8-Bit Microcontroller with MASK ROM

Product Specification (V1.3) 07.29.2004

• 25

(This specification is subject to change without further notice)

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

Bit 0 (LVDD

Levels of the Operating Voltage.

0: Operating Voltage 2.3V ~ 5.5V, non-power saving.

1: Operating Voltage 4V ~ 5.5V, power saving.

Bit 1 (CLK)

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)

Bit 5

Reserved.

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

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