EM78159NAS EMC [ELAN Microelectronics Corp], EM78159NAS Datasheet - Page 36

• Manufacturer Part Number: EM78159NAS
• Description: 8-Bit Microcontroller with OTP ROM
• Manufacturer: EMC [ELAN Microelectronics Corp]

EM78P159N
8-Bit Microcontrollerwith OTP ROM
32 •
4.9 Power On Considerations
4.10 External Power On Reset Circuit
Bit 6 (CYES):
Bit 7 ~ Bit 10:
Bits 11 (RCOUT): System clock output enable bit in IRC or ERC mode
Bit 12:
4.8.3 Customer ID Register (Word 2)
Bit 0 ~ Bit 12: User’s ID code
Any microcontroller is not guaranteed to start to operate properly before the power
supply stays at its steady state.
EM78P159N POR voltage range is 1.7V~1.9V. Under customer application, when
power is OFF, Vdd must drop to below 1.2V and remains OFF for 10µs before power
can be switched ON again. This way, the EM78P159N will reset and operates
normally. The extra external reset circuit will work well if Vdd can rise at very fast speed
(50 ms or less). However, under most cases where critical applications are involved,
extra devices are required to assist in solving the power-up problems.
The circuit shown in the
following figure imple-
ments an external RC to
produce the reset pulse.
The pulse width (time
constant) should be kept
long enough for Vdd to
reached minimum opera-
tion voltage. This circuit is
used when the power
supply has a 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.
Bit12 Bit11 Bit10
-
-
-
Instruction cycle selection bit
0 = one instruction cycle
1 = two instruction cycles (default)
Not used
0 = OSCO pin is open drain.
1 = OSCO output system clock
Not used
Bit9
-
Bit8
-
EM78P159N
Bit7
-
(This specification is subject to change without further notice)
/RESET
Figure 4-10 External Power-Up Reset Circuit
WORD 0
Vdd
Bit6
-
Bit5
Product Specification (V1.0) 03.10.2006
-
Bit4
-
Rin
Bit3
-
R
C
Bit2
-
Bit1
-
D
Bit0
-