Usage Notes On The 8/10-Bit A/D Converter - Fujitsu MB90460 Series Hardware Manual

20.7

Usage Notes on the 8/10-bit A/D Converter

Notes on using the 8/10-bit A/D converter.
■ Usage Notes on the 8/10-bit A/D Converter
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Analog input pin
The A/D input pins are also used as the I/O pins of port 5. The port 5 data register (DDR5) and analog
input enable register (ADER) determine which pin is used for which purpose.
To use a pin as analog input, write "0" to the corresponding bit of DDR5 and change the port setting to
input. Then, set the analog input mode (ADEx = 1) in the ADER register and determine the input gate of
the port.
If an intermediate-level signal is input in the port input mode (ADEx = 0), a leakage current flows through
the gate.
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Note on using an internal timer
To start the A/D converter with an internal timer, set the STS1 and STS0 bits of A/D control status register
1 (ADCS1) accordingly. Set the input value of the internal timer at the inactive level (L for the internal
timer). Otherwise, operation may start concurrently with writing to the ADCS register.
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Sequence of turning on the A/D converter and analog input
Do not turn on power to the A/D converter (AVcc, AVR) and to the analog inputs (AN0 to AN7) before the
digital power supply (Vcc) has been turned on.
Do not turn off the digital power supply (Vcc) before power to the A/D converter and the analog inputs has
been turned off.
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Supply voltage to the A/D converter
The supply voltage to the A/D converter (AVcc) must not exceed the digital power supply (Vcc);
otherwise, latch-up may occur.
CHAPTER 20 8/10-BIT A/D CONVERTER
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