em78p809n ELAN Microelectronics Corp, em78p809n Datasheet - Page 63

• Manufacturer Part Number: em78p809n
• Description: 8-bit Microcontroller
• Manufacturer: ELAN Microelectronics Corp

Product Specification (V1.0) 07.26.2005
(This specification is subject to change without further notice)
4.18 Power-on Considerations
4.17.2 Customer ID Register
4.18.1 External Power-on Reset Circuit
PR2~PR0 are write-protect bits, configured as follow s:
Bits 12 ~ 0: Customer’s ID code
Any microcontroller is not guaranteed to start and operate properly before the power
supply maintains at its steady state. The EM78P809N has a built-in Power On Voltage
Detector (POVD) with a detecting level of 2.1V. It will work well if V
(10 ms or less). In many critical applications, however, additional components are
required to provide solutions on probable power-up problems.
The circuit shown in Fig. 34 use an external RC to produce the reset pulse. The pulse
width (time constant) should be kept long enough for V
voltage. This circuit is used when the power supply has slow rise time. Because the
Bit 6 (CYES) : Cycle selection for JMP, CALL instruction
Bit 4 (OSC) : Oscillator type selection.
Bit 3 (HLP) : Power selection.
Bit 2~0 (PR2~PR0) : Protect Bit
PR2
1
OSC = “0” : RC type
OSC = “1” : Crystal type
CYES = “0” : One cycle
CYES = “1” : Two cycles
HLP = “0” : Low power
HLP = “1” : High power
Others
PR1
1
XXXXXXXXXXXXX
XXXXXXXXXXXXX
Bit 12~Bit 0
Bit 12~Bit 0
Word 1
Word 2
PR0
1
DD
to reach minimum operation
8-Bit Microcontroller
DD
Protect
Disable
Enable
rises fast enough
EM78P809N
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