ST10F276E
A/D converter
13
A/D converter
A 10-bit A/D converter with 16+8 multiplexed input channels and a sample and hold circuit is
integrated on-chip. An automatic self-calibration adjusts the A/D converter module to
process parameter variations at each reset event. The sample time (for loading the
capacitors) and the conversion time is programmable and can be adjusted to the external
circuitry.
The ST10F276E has 16+8 multiplexed input channels on Port 5 and Port 1. The selection
between Port 5 and Port 1 is made via a bit in a XBus register. Refer to the user manual for
a detailed description.
A different accuracy is guaranteed (Total Unadjusted Error) on Port 5 and Port 1 analog
channels (with higher restrictions when overload conditions occur); in particular, Port 5
channels are more accurate than the Port 1 ones. Refer to Chapter 23: Electrical
characteristics for details.
The A/D converter input bandwidth is limited by the achievable accuracy: supposing a
maximum error of 0.5 LSB (2mV) impacting the global TUE (TUE depends also on other
causes), in worst case of temperature and process, the maximum frequency for a sine wave
analog signal is around 7.5 kHz. Of course, to reduce the effect of the input signal variation
on the accuracy down to 0.05 LSB, the maximum input frequency of the sine wave shall be
reduced to 800 Hz.
If static signal is applied during sampling phase, series resistance shall not be greater than
20kΩ (this taking into account eventual input leakage). It is suggested to not connect any
capacitance on analog input pins, in order to reduce the effect of charge partitioning (and
consequent voltage drop error) between the external and the internal capacitance: in case
an RC filter is necessary the external capacitance must be greater than 10nF to minimize
the accuracy impact.
Overrun error detection / protection is controlled by the ADDAT register. Either an interrupt
request is generated when the result of a previous conversion has not been read from the
result register at the time the next conversion is complete, or the next conversion is
suspended until the previous result has been read. For applications which require less than
16+8 analog input channels, the remaining channel inputs can be used as digital input port
pins.
The A/D converter of the ST10F276E supports different conversion modes:
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Single channel single conversion: The analog level of the selected channel is
sampled once and converted. The result of the conversion is stored in the ADDAT
register.
Single channel continuous conversion: The analog level of the selected channel is
repeatedly sampled and converted. The result of the conversion is stored in the ADDAT
register.
Auto scan single conversion: The analog level of the selected channels are sampled
once and converted. After each conversion the result is stored in the ADDAT register.
The data can be transferred to the RAM by interrupt software management or using the
powerful Peripheral Event Controller (PEC) data transfer.
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Auto scan continuous conversion: The analog level of the selected channels are
repeatedly sampled and converted. The result of the conversion is stored in the ADDAT
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