Section 23
A/D Converter
Rev. 1.00 Mar. 12, 2008 Page 911 of 1178
REJ09B0403-0100
23.7 Usage
Notes
23.7.1
Setting of Module Stop Mode
Operation of the A/D converter can be enabled or disabled by setting the module stop control
register. By default, the A/D converter is stopped. Registers of the A/D converter only become
accessible when it is released from module stop mode. See section 28, Power-Down Modes, for
details.
23.7.2 Permissible
Signal Source Impedance
This LSI’s analog input is designed so that the conversion accuracy is guaranteed for an input
signal for which the signal source impedance is 5 k
Ω
or less. This specification is provided to
enable the A/D converter’s sample-and-hold circuit input capacitance to be charged within the
sampling time; if the sensor output impedance exceeds 5 k
Ω
, charging may be insufficient and it
may not be possible to guarantee the A/D conversion accuracy. However, if a large capacitance is
provided externally in single mode, the input load will essentially comprise only the internal input
resistance of 10 k
Ω
, and the signal source impedance is ignored. However, since a low-pass filter
effect is obtained in this case, it may not be possible to follow an analog signal with a large
differential coefficient (voltage fluctuation ratio of 5 mV/µs or greater for example) (see figure
23.8). When converting a high-speed analog signal or converting in scan mode, a low-impedance
buffer should be inserted.
A/D converter equivalent circuit
This LSI
20 pF
C
in
=
15 pF
10 k
Ω
up to 5 k
Ω
Low-pass
filter C
up to 0.1 µF
Sensor output
impedance
Sensor input
Figure 23.8 Example of Analog Input Circuit
Summary of Contents for H8S Family
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Page 70: ...Section 1 Overview Rev 1 00 Mar 12 2008 Page 22 of 1178 REJ09B0403 0100...
Page 108: ...Section 2 CPU Rev 1 00 Mar 12 2008 Page 60 of 1178 REJ09B0403 0100...
Page 116: ...Section 3 MCU Operating Modes Rev 1 00 Mar 12 2008 Page 68 of 1178 REJ09B0403 0100...
Page 152: ...Section 5 Interrupt Controller Rev 1 00 Mar 12 2008 Page 104 of 1178 REJ09B0403 0100...
Page 206: ...Section 6 Bus Controller BSC Rev 1 00 Mar 12 2008 Page 158 of 1178 REJ09B0403 0100...
Page 420: ...Section 9 14 Bit PWM Timer PWMX Rev 1 00 Mar 12 2008 Page 372 of 1178 REJ09B0403 0100...
Page 476: ...Section 12 Watchdog Timer WDT Rev 1 00 Mar 12 2008 Page 428 of 1178 REJ09B0403 0100...
Page 552: ...Section 14 CRC Operation Circuit CRC Rev 1 00 Mar 12 2008 Page 504 of 1178 REJ09B0403 0100...
Page 712: ...Section 18 I2 C Bus Interface IIC Rev 1 00 Mar 12 2008 Page 664 of 1178 REJ09B0403 0100...
Page 804: ...Section 19 LPC Interface LPC Rev 1 00 Mar 12 2008 Page 756 of 1178 REJ09B0403 0100...
Page 838: ...Section 20 Ethernet Controller EtherC Rev 1 00 Mar 12 2008 Page 790 of 1178 REJ09B0403 0100...
Page 964: ...Section 24 RAM Rev 1 00 Mar 12 2008 Page 916 of 1178 REJ09B0403 0100...
Page 1066: ...Section 25 Flash Memory Rev 1 00 Mar 12 2008 Page 1018 of 1178 REJ09B0403 0100...
Page 1098: ...Section 26 Boundary Scan JTAG Rev 1 00 Mar 12 2008 Page 1050 of 1178 REJ09B0403 0100...
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