EM78P156E Ver la hoja de datos (PDF) - ELAN Microelectronics
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EM78P156E Datasheet PDF : 28 Pages
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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.
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.
VDD
/RESET
EM78P156E
Rin
R
D
C
Fig. 14 External Power-up Reset Circuit
* This specification is subject to be changed without notice. 8.11.1999
B3-21
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