EM78P312N
8-Bit Microcontroller
Bit 4 (OSC) : Oscillator type selection
OSC = “0” : RC type
OSC = “1” : Crystal type
Bit 3 (HLP) : Power selection
HLP = “0” : Low power
HLP = “1” : High power
Bit 2~0 (PR2~PR0) : Protect Bit
PR2~PR0 are write-protect bits, configured as follows:
PR2
PR1
Others
1
PR0
Protect
Enable
Disable
1
1
5.17.2 Customer ID Register
Word 1
Bit 12~Bit 0
XXXXXXXXXXXXX
Word 2
Bit 12~Bit 0
XXXXXXXXXXXXX
Bits 12 ~ 0: Customer’s ID code
5.18 Power-on Considerations
Any microcontroller is not guaranteed to start and operate properly before the power
supply maintains at its steady state. The EM78P312N has a built-in Power On Voltage
Detector (POVD) with a detecting level of 2.1V. It will work well if VDD rises fast enough
(10 ms or less). In many critical applications, however, additional components are
required to provide solutions on probable power-up problems.
5.18.1 External Power-on Reset Circuit
The circuit shown in Fig. 5-33 use an external RC to produce the reset pulse. The
pulse width (time constant) should be kept long enough for VDD to reach 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 5μA, it is recommended
that R should not be greater than 40K. In this way, the /RESET pin voltage is held
below 0.2V. The diode (D) acts as a short circuit at the moment of power down. The
capacitor C will discharge rapidly and fully. Rin, the current-limited resistor, will prevent
high current or ESD (electrostatic discharge) from flowing to pin /RESET.
54 •
Product Specification (V1.0) 10.03.2006
(This specification is subject to change without further notice)
ELAN [ ELAN MICROELECTRONICS CORP ]
