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THROUGH THE LOOKING GLASS

Taking a Look at the PIC18Cxxx Series
by David Brobst

Start ý PIC18Cxxx Chips ý Memory ý Data Memory ý Advanced Indirect Addressing ý Deep and Accessible Stack ý Interrupts ý Power-On Features ý Clock Speed ý 10-Bit A/D ý Hardware Multiplier ý Timers ý CCP/PWM ý USART ý I²C Master ý Table Read/Write ý Current Status ý Sources and PDF

10-BIT A/D

The A/D unit on the PIC18Cxxx family is 10 bits. This is about 60 dB of signal-to-noise ratio for the A/D. This allows the controller to be used in higher precision systems than the mid-range PIC devices. The A/D functions just like the A/D units in the mid-range devices but with the added two bits. The results of the A/D span two 8-bit registers but can be justified to the MSB or LSB, depending on your needs.

The other interesting and useful feature of the A/D unit is that both the high and low references can be externally input. This allows the A/D unit to automatically take out an unwanted DC offset. For example, if a signal entered the A/D unit with a range of 2.5 to 4 V, the positive reference could be set to 4.096 V and the negative reference to 2.5 V to isolate the incoming voltage in the window of interest. This eases the demands on external conditioning circuitry on the front end of the A/D.

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