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App8: SPI ADC
Purpose
Provide a program that interfaces to an analog to digital converter through the SPI port. This example uses the LTC1298, a 12 bit two channel ADC.
Description
This program initializes thirteen i⁄o lines of the U401⁄U421⁄U451 to be outputs, and enables the SPI subsystem. The LTC1298, a 12 bit serial (SPI) A⁄D device, is connected to the MISO, MOSI, and CLK lines, as well as one of the output lines. The program selects the ADC device, selects channel 0, and reads the converted analog value. This is repeated for channel 1.
See this small list of SPI devices for other SPI A⁄D devices.
Screen Shot
Below is the application screen reading some A⁄D values.
Hardware
The data sheet for the LTC1298 was followed for connection to the U4x1 device. Bypass capacitors are not shown in the schematic.
Pin 1 of the LTC1298 is the active low chip select and is controlled by port A.4. MOSI of the U4x1 (A.5) connects to the A⁄D "D in" to send a command to the A⁄D, while MISO (A.6) reads the data from "D out". The SPI clock (A.7) connects to pin 7, the LTC1298's clock line.
Code
Download all application files: (all application files)
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