Page 140 of 346 Start Back Next End ZBasic System Library 128 ZBasic Microcontrollers GetADC (subroutine form) Type Subroutine Invocation GetADC(pin, val) GetADC(pin, val, fullScale) GetADC(pin, val, fullScale, offset) Parameter Method Type Description pin ByVal Byte The pin from which to read an analog voltage. Val ByRef Single The variable in which to return the result. fullScale ByVal Single The full-scale voltage value. offset ByVal Integral The offset to apply before scaling. Discussion This function performs an analog-to-digital conversion on the signal present on the specified pin that must be one of the analog port pins (see the table below). The return value will be a 10-bit (for ATxmega- based devices) or 12-bit (for ATxmega-based devices) digital approximation of the input voltage with a range from zero to the reference voltage (see below). For the first form, the returned value is scaled to the range 0.0 to 1.0 and for the remaining forms it is scaled to the range 0.0 to value of the fullScale parameter. For the third form, the value of the offset parameter (which could be negative) is added to the 10-bit ADC value before scaling. This is useful, for example, for removing the effect of a non-zero offset voltage of the ADC. You must make the pin an input before calling this routine. For ATtiny and ATmega target devices, the conversion is performed using the AVcc reference voltage (connected internally to Vcc on the ZX-24, ZX-24a, ZX-24p, ZX-24n, ZX-24r, ZX-24s, ZX-24e, ZX-24ae, ZX-24ne, ZX-24pe, ZX-24nu, ZX-24pu, ZX-24ru, ZX-24su, ZX-328nu, ZX-128e, ZX-128ne, ZX-1281e and ZX-1281ne). For ATxmega target devices, the conversion is performed using a reference voltage of Vcc/1.6. Resource Usage Only analog port pins may be used to perform an analog-to-digital conversion. The number and location of analog port pins vary depending on the ZBasic target device. See the section Analog-to-Digital Converters for more information. Most ZBasic target devices contain a single analog-to-digital converter thus allowing only one conversion to be performed at a time (some have none at all). The conversion process takes approximately 220uS during which time the calling task will be awaiting conversion completion. Compatibility Although the BasicX manual indicates that that it is not necessary to configure the pin to be an input before calling, tests indicate that it is, in fact, necessary to do so. Consequently, the behavior of this implementation matches the actual behavior of the BasicX platform. The second and third forms are not available in BasicX mode.