APPENDIX C MOUNTING PRECAUTIONS
AP-C-4
Seiko Epson Corporation
S1C33L26 TECHNICAL MANUAL
(4) #NMI pin
Low-level noise to this pin causes an NMI interrupt. Due to the circuit design, this situation tends to occur
when the #NMI pin is in the high state, with high impedance. Lower the impedance of #NMI when it is
held high, or incorporate corrective measures into the software to protect against erratic operations.
(5)
*
V
DD
and V
SS
power supply
The IC will malfunction at the instant when noise falling below the rated voltage is input. Incorporate coun-
termeasures on the circuit board, including close patterns for circuit board power supply circuits, noise-
filtering decoupling capacitors, and surge/noise prevention components on the power supply line.
Perform the inspections described above using an oscilloscope capable of observing waveforms of at least 200
MHz. It may not be possible to observe high-speed noise events with a low-speed oscilloscope.
If you detect potential noise-induced malfunctions while observing the waveform with an oscilloscope, recheck
with a low-impedance (less than 1 k
W
) resistor connecting the relevant pin to GND or to the power supply.
Malfunctions at that pin are likely if changes are visible, such as the malfunction disappearing, becoming less
frequent, or the phenomena changing.
The TEST, DSIO, #RESET, and #NMI input circuits described above detect input signal edges and are suscep-
tible to malfunctions induced by spike noise. This makes these digital signal pins the most susceptible to noise.
To reduce potential noise, keep the following two points in mind when designing circuit boards:
(A) It is important to lower the signal-driving impedance, as described above. Connect pins to the power supply
or GND, with impedance of 1 k
W
or less, preferably 0
W
. The signal lines connected should be no longer
than approximately 5 mm.
(B) Parallel routing of signal lines with other digital lines on the board is undesirable, since the noise generated
when the signal changes from High to Low or vice versa may adversely affect the digital lines. The sig-
nal may be subject to the most noise when signal lines are laid between multiple signal lines whose states
change simultaneously. Take corrective measures by shortening the parallel distance (to several cm) or
separating signal lines (2 mm or more).
Handling of light (for bare chip mounting)
The characteristics of semiconductor components can vary when exposed to light. ICs may malfunction or non-
volatile memory data may be corrupted if ICs are exposed to light.
Consider the following precautions for circuit boards and products in which this IC is mounted to prevent IC
malfunctions attributable to light exposure.
(1) Design and mount the product so that the IC is shielded from light during use.
(2) Shield the IC from light during inspection processes.
(3) Shield the IC on the upper, underside, and side faces of the IC chip.
(4) Mount the IC chip within one week of opening the package. If the IC chip must be stored before mounting,
take measures to ensure light shielding.
(5) Adequate evaluations are required to assess nonvolatile memory data retention characteristics before prod-
uct delivery if the product is subjected to heat stress exceeding regular reflow conditions during mounting
processes.