aPPenDiX D MeaSuReS aGainST nOiSe
S1C17153 TeChniCal Manual
Seiko epson Corporation
aP-D-1
(Rev. 1.0)
Appendix D Measures Against Noise
To improve noise immunity, take measures against noise as follows:
noise Measures for V
DD
and V
SS
Power Supply Pins
The IC will malfunction at the instant when noise falling below the rated voltage is input. Take measures on the
circuit board, including close patterns for circuit board power supply circuits, noise-filtering decoupling capaci-
tors, and surge/noise prevention components on the power supply line.
For the recommended patterns on the circuit board, see “Mounting Precautions” in Appendix.
noise Measures for #ReSeT Pin
The pull-up resistor for the #RESET pin included in this product has a relatively high impedance of 100 k
W
to
500 k
W
and is not noise-resistant. Extraneous noise may pull the #RESET pin down to a low level and this will
cause the IC to reset. Therefore, the circuit board must be designed properly taking noise measures into consid-
eration.
For the recommended patterns on the circuit board, see “Mounting Precautions” in Appendix.
noise Measures for Oscillator Pins
The oscillator input pins must pass a signal of small amplitude, so they are hypersensitive to noise. Therefore,
the circuit board must be designed properly taking noise measures into consideration.
For the recommended patterns on the circuit board, see “Mounting Precautions” in Appendix.
noise Measures for interrupt input Pins
This product is able to generate a port input interrupt when the input signal changes. The interrupt is generated
when an input signal edge is detected, therefore, an interrupt may occur if the signal changes due to extraneous
noise.
To prevent occurrence of unexpected interrupts due to extraneous noise, enable the chattering filter circuit when
using the port input interrupt.
For details of the port input interrupt and chattering filter circuit, see the “I/O Ports (P)” chapter.
noise Measures for uaRT Pins
This product includes a UART module for asynchronous communications. The UART starts receive operation
when it detects a low level input from the SIN
x
pin. Therefore, a receive operation may be started if the SIN
x
pin is set to low due to extraneous noise. In this case, a receive error will occur or invalid data will be received.
To prevent UART from malfunction caused by extraneous noise, take the following measures:
• Stop the UART operations (RXEN/UART_CTL
x
register = 0) while asynchronous communication is not per-
formed.
• Execute the resending process via software after executing the receive error handler with a parity check.
For details of the pin functions and the function switch control, see the “I/O Ports (P)” chapter. For the UART
control and details of receive errors, see the “UART” chapter.
