參數(shù)資料
型號(hào)： UPD17240MC-XXX-5A4-A
元件分類： 微控制器/微處理器
英文描述： 4-BIT, MROM, 8 MHz, MICROCONTROLLER, PDSO30
封裝： 0.300 INCH, PLASTIC, SSOP-30
文件頁(yè)數(shù)： 55/102頁(yè)
文件大小： 668K
代理商： UPD17240MC-XXX-5A4-A
56
Data Sheet U15002EJ1V0DS
PD17240, 17241, 17242, 17243, 17244, 17245, 17246
5.3.2
Countermeasures against noise during transmission (carrier output)
When a signal is transmitted from the transmitter of a remote controller, a peak current of 0.5 to 1 A may flow through
the infrared LED. Since two batteries are usually used as the power source of the transmitter, several
of equivalent
resistance (r) exists in the power source as shown in Figure 5-2. This resistance increases to 10 to 20
if the supply
voltage drops to 2 V. While the carrier is being output from the REM pin (while the infrared LED lights), therefore,
a high-frequency noise may be generated on the power lines due to the voltage fluctuation that may take place
especially during switching.
To minimize the influence on the microcontroller of this high-frequency noise, take the following measures.
<1> Separate the power lines of the microcontroller from the power lines of the infrared LED with the terminals
of the batteries at the center. Use thick power lines and keep the wiring short.
<2> Locate the resonator as close as possible to the microcontroller and shield it with GND lines (as indicated
by the shaded portion in the figure below).
<3> Locate the capacitor for stabilization of the power supply closely to the power lines of the microcontroller.
Also, use a capacitor to eliminate high-frequency noise.
<4> To prevent data from changing, do not execute data read/write processing such as key scan, an interrupt
that requires a stack, or the CALL/RET instruction, while the carrier is being output.
<5> To improve the reliability in case of program hang-up, use the watchdog timer.
Figure 5-2. Example of Countermeasures Against Noise
0.5 to 1 A
Infrared LED
REM
VDD
Microcontroller
+
–
r
Batteries
VSS
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