Syntax:
For a normal (also called a Single Channel) read, use:
word_variable = ReadAD10( ANX )
For a Differential Channel read, use the following, where ANpX is the positive port and ANnY is the negative port:
integer_variable = ReadAD10( ANpX , ANnY )
To force a 10-bit AD channel to always respond with a value in the range [0 to 1023], use:
integer_variable = ReadAD10( ANX , TRUE )
Command Availability:
ReadAD10 is a function that reads the built-in analog-to-digital converter (ADC) that most microcontroller chips include. The port
is specified as AN0, AN1, AN2, and so on, up to the number of analog inputs available on the chip in use. Those familiar with Atmel AVR microcontrollers
can also refer to the ports as ADC0, ADC1, and so on — refer to the chip’s datasheet to find the number of ports available. (Note: it is perfectly acceptable to use
ANx on AVR, or ADCx on a Microchip PIC.)
When using ReadAD10( ANX ), the returned value is the full range of the ADC module. The method returns an 8-bit value [0-255], a 10-bit value [0-1023], or a 12-bit value [0-4095] depending
on the microcontroller’s capabilities. To guarantee a 10-bit value [0-1023] regardless of the chip, use user_variable = ReadAD10( ANX , TRUE ) instead. The receiving variable can be a byte, word, integer, or long, but a word is typically recommended.
When using ReadAD10( ANpX , ANnY ) for a differential reading, the returned value is an integer, since negative values can be returned.
When using ReadAD10( ANpX , TRUE ) to force a 10-bit reading, the returned value is also an integer.
Other functions with similar behaviour are ReadAD and ReadAD12 — see their Help pages for the specific usage of each.
AD_DELAY controls the acquisition delay: the time the ADC’s internal holding capacitor is given to charge to the input voltage before
the reading is taken. The default value is 20 us. If a reading looks noisy or consistently off — especially from a high-impedance
sensor, such as a bare voltage divider without a buffer — increasing this delay is often the fix, since the capacitor needs
more time to settle. Change it with:
#define AD_DELAY 4 10us
ADSPEED controls the source of the clock for the ADC module; it varies from one chip to another. InternalClock is a microcontroller-only option that drives the ADC from an internal RC oscillator. The default value is 128.
'default value
#define ADSPEED MEDIUMSPEED
'pre-defined constants
#define HIGHSPEED 255
#define MEDIUMSPEED 128
#define LOWSPEED 0AD_ACQUISITION_TIME_SELECT_BITS also controls the acquisition time select bits. Acquisition time is the duration the ADC’s charge-holding capacitor stays
connected to the AD channel, from the moment the read starts until conversion begins — the same underlying delay that AD_DELAY adjusts, exposed here as the raw bit pattern for microcontrollers whose datasheet documents it this way.
The default value of AD_ACQUISITION_TIME_SELECT_BITS is 0b100 (decimal 4), which sets all three ACQT bits. To change it:
'change the default value
#define AD_ACQUISITION_TIME_SELECT_BITS 0b001 'this will only set ACQT bit 0; ACQT bits 1 and 2 will be clearedExample 1 - Read 10-bit ADC
#chip 16F819, 8
'Set the input pin direction
Dir PORTA.0 In
'Print 255 readings
For CurrentAddress = 0 to 255
'Take a reading and show it
Print str(ReadAD10(AN0)) ' <<< the ReadAD10 instruction
'Wait 10 minutes before getting another reading
Wait 10 min
NextKey line: Print str(ReadAD10(AN0)) — reads channel AN0 and returns whatever resolution the chip’s ADC module natively supports (8, 10, or 12 bits).
Example 2 - Reading Reference Voltages
When selecting the reference source for the ADC on an ATmega328, GCBASIC overwrites anything written directly into the ADMUX register — but this option lets you change the ADC reference source on Atmel AVR microcontrollers. Set the AD_REF_SOURCE constant to whichever reference you want to use. It defaults to the VCC pin; for example, you can set the Atmel AVR to use
the 1.1V reference with #define AD_REF_SOURCE AD_REF_256, where 256 refers to the 2.56V reference on some older AVRs, though the same code selects the 1.1V reference on an ATmega328P.
'Dynamically switching reference.
#define AD_REF_SOURCE ADREFSOURCE
#define AD_VREF_DELAY 5 ms
ADREFSOURCE = AD_REF_AVCC
HSerPrint ReadAD10(AN1)
HSerPrint ", "
ADREFSOURCE = AD_REF_256 ' <<< switching the ADC reference source at run time
HSerPrint ReadAD10(AN1)Key line: ADREFSOURCE = AD_REF_256 — changes which reference voltage the next ReadAD10 call uses. After switching references, allow AD_VREF_DELAY for the reference capacitor to charge to the new voltage before trusting the reading.
Example 3 - Force a 10-bit value to be returned
#chip 16F1789, 8
'Set the input pin direction
Dir PORTA.0 In
'Print 255 readings
For CurrentAddress = 0 to 255
'Take a reading and show it
Print str(ReadAD10(AN0), TRUE) ' <<< forcing a 10-bit result regardless of the chip's native ADC resolution
'Wait 10 minutes before getting another reading
Wait 10 min
NextKey line: ReadAD10(AN0), TRUE — the TRUE argument guarantees a value in the range [0-1023] even on a chip whose ADC natively returns 8 or 12 bits.
Example 4 - Differential reading
This example uses the differential capabilities of the ADC and writes the output to a serial terminal. The output value will
be in the range [-1023 to 1023]. AN0 and AN2 are used for the differential reading.
#chip 16F1789, 8
'USART settings
#define USART_BAUD_RATE 9600 'Initializes USART port with 9600 baud
#define USART_TX_BLOCKING 'wait for tx register to be empty
wait 100 ms
'Set the input pin direction
Dir PORTA.0 In
Dir PORTA.2 In
'Loop to take readings until the EEPROM is full
For CurrentAddress = 0 to 255
'Take a reading and log it
HSerPrint ReadAD10( AN0, AN2 ) ' <<< the differential ReadAD10 instruction
HserPrintCRLF
'Wait 10 minutes before getting another reading
Wait 10 min
NextKey line: ReadAD10( AN0, AN2 ) — reads the voltage difference between AN0 (positive) and AN2 (negative) as a signed integer, rather than an absolute voltage on a single pin.
See Also:
