IBM EM78P312N Power-on Considerations, Customer ID Register, External Power-on Reset Circuit

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:

PR2PR1

PR0

Protect

	Others		Enable
1	1	1	Disable

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)