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13.6
Precautions when Using 8-/10-bit A/D Converter
Precautions when using the 8-/10-bit A/D converter are given below:
I Precautions when Using 8-/10-bit A/D Converter
G
Analog input pin
• The analog input pins serve as a general-purpose I/O port of the port 5.To use the pin as an analog input
pin, set the port-5 direction register (DDR5) and analog input enable register (ADER) to switch it to an
analog input pin.
• When using the pin as an analog input pin, write "0" to the bit in the port 5 direction register (DDR5)
corresponding to the pin to be used and turn off the output transistor. Also write "1" to the bit in the
ADER corresponding to the pin to be used and set the pin to analog input enable.
• When an intermediate-level signal is input with the pin set as a general-purpose I/O port, the input
leakage current flows in the gate. When using the pin as an analog input pin, always set the pin to
analog input enable.
G
Precaution when starting by internal timer or external trigger
• The input value at which the 8-/10-bit A/D converter is started by the internal timer output or external
trigger should be set to inactive (High for external trigger).Holding the input value for the start trigger
active may cause the 8-/10-bit A/D converter to start concurrently with the setting of the A/D start
trigger select bits in the A/D control status register (ADCS: STS1, STS0).
G
Procedure of 8-/10-bit A/D converter and analog input power-on
• Always apply a power to the A/D converter power and the analog input (AN0 to AN7 pins) after or
concurrently with the digital power (V
• Always turn off the A/D converter power and the analog input before or concurrently with the digital
power-down.Note that AVR should not exceed AV
G
Power supply voltage of 8-/10-bit A/D converter
• To prevent latch up, note that the 8-/10-bit A/D converter power (AV
power (V
) voltage.
CC
CHAPTER 13 8/10-bit A/D converter
)-on.
CC
at power on or power down.
CC
) should not exceed the digital
CC
379
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