B3-21

EM78P156E

1: XTAL1 type (High frequency)

This bit will affect system oscillation only when Bit 12 (MS) is “1”. When MS is “0”, HLF must be “0”.

Bit 7 (IRCEN): RC oscillator selection.

0: R connected to Vdd with internal C.

1: External RC

Bit 6 (HLP): Power selection.

0: Low power

1: High power

Bits 5 ~ 0: Not used.

2.

User’s ID Register

The EM78P156E has one User’s ID register which is not a part of the normal program memory. The User’s ID bits

can not be accessed during normal program execution.

12 ~0

XXXXXXXXXXXXX

Bit 12 ~ 0: User’s ID code.

D

R

Rin

C

VDD

/RESET

EM78P156E

Fig. 14 External Power-up Reset Circuit

VI.9 Power-on Considerations

Any microcontroller is not warranted to start proper operation before the power supply stays in its steady state.

EM78P156E is equipped with Power On Voltage Detector (POVD) which the detective level is about 1.8V. It

will work well if Vdd rises quickly enough (50ms or less). In many critical applications; however, extra devices

are still required to assist in solving power-up problems.

VI.10 External Power-on Reset Circuit

The circuit shown in Fig.14 implements an external RC to produce the reset pulse. The pulse width (time constant)

should keep long enough until Vdd has reached minimum operation voltage. This circuit is used when the power supply

has slow rise time. Because the current leakage from the /RESET pin is about 5A, it is recommended that R should

not be greater than 40K. In this way, the voltage in pin /RESET will be held below 0.2V. The diode (D) acts a short circuit

at the moment of power-down. The capacitor, C, will be discharged rapidly and fully. Rin, the current-limited resistor,

protects against a high discharging current or ESD (electrostatic discharge) flowing to pin /RESET.