HD6432670 Hitachi, HD6432670 Datasheet - Page 774

• Manufacturer Part Number: HD6432670
• Description: (HD64F267x Series) 16-Bit Microcomputer
• Manufacturer: Hitachi

16.7.5
In board design, digital circuitry and analog circuitry should be as mutually isolated as possible,
and layout in which digital circuit signal lines and analog circuit signal lines cross or are in close
proximity should be avoided as far as possible. Failure to do so may result in incorrect operation
of the analog circuitry due to inductance, adversely affecting A/D conversion values.
Also, digital circuitry must be isolated from the analog input signals (AN0 to AN7 and AN12 to
AN15), analog reference power supply (Vref), and analog power supply (AVcc) by the analog
ground (AVss). Also, the analog ground (AVss) should be connected at one point to a stable
digital ground (Vss) on the board.
16.7.6
A protection circuit connected to prevent damage due to an abnormal voltage such as an excessive
surge at the analog input pins (AN0 to AN7 and AN12 to AN15) should be connected between
AVcc and AVss as shown in figure 16.7. Also, the bypass capacitors connected to AVcc and the
filter capacitor connected to AN0 to AN7 and AN12 to AN15 must be connected to AVss.
If a filter capacitor is connected, the input currents at the analog input pins (AN0 to AN7 and
AN12 to AN15) are averaged, and so an error may arise. Also, when A/D conversion is
performed frequently, as in scan mode, if the current charged and discharged by the capacitance of
the sample-and-hold circuit in the A/D converter exceeds the current input via the input impedance
(R
when deciding the circuit constants.
Rev. 2.0, 04/02, page 728 of 906
in
), an error will arise in the analog input pin voltage. Careful consideration is therefore required
Notes on Board Design
Notes on Noise Countermeasures