AT91SAM7A2_04 Datasheet, PDF (108/369 Pages) ATMEL Corporation – AT91 ARM Thumb-based Microcontrollers

PRELIMINARY
10-bit Analog to Digital Converter (ADC)
Overview
The AT91SAM7A2 includes two 10-bit ADCs (8 channels).
The 10-bit Analog to Digital Converter (ADC) can be configured in different modes as
follows.
• Single input/one shot mode: One input selected and a single conversion.
• Single input/continuous mode: One input selected, the microprocessor gives the
first start to the peripheral which is then completely independent. The PDC can be
used to save the resulting data in memory.
The conversion is stopped in two ways:
1. By the microprocessor, by setting the STOP bit of the active control register.
2. By the PDC: TEND can stop the conversion if the STOPEN bit of the mode
register is active. This allows the user to order a conversion of a certain num-
ber of data without any software intervention.
• Multiple input/one shot mode: The user selects which analog inputs will be
converted and specifies the names of the inputs that will be considered by the ADC
and in which order they will be converted. This allows the user to make conversions
of some of the eight inputs in the order of preference, in one shot. The PDC can be
used to save each result.
• Multiple input/continuous mode: Several analog inputs are converted, the
microprocessor first starts up the peripheral which then becomes completely
independent.
The conversion is stopped in two ways:
– By the microprocessor, by setting the STOP bit of the active control register.
– By the PDC: TEND can stop the conversion if the STOPEN bit of the mode
register is active. This allows the user to order a conversion of a certain
number of data without any software intervention.
If the PDC is active, a flag is set when the transfer of all the data is finished.
The converter is composed of a 10-bit cascaded potentiometric digital to analog con-
verter connected to the negative input of a Sample and Hold comparator. It is based on
a string of 64 polysilicon resistors connected between reference inputs VREF. So, the
analog input to be converted needs to be in the interval [GND:VREFP].
In the terminology, the Integral Non-Linearity (INL) is a measure of the maximum devia-
tion from a straight line passing through the end-points of the transfer function. It does
not include the full scale error and the zero error. It is calculated from the real value of
the LSB which is calculated from the output range (output variation between the minimal
value 0 and the maximal one).
The Differential Non-linearity (DNL) is the difference between the measured change and
the ideal change between any two adjacent codes. A specified DNL of ±1 LSB max over
the operating point temperature range ensures monotony. The DNL is relative to the real
value of the LSB.
108 _AT91SAM7A2
6021A–ATARM–07/04