THE MAGAZINE FOR COMPUTER APPLICATIONS
Circuit Cellar Online offers articles illustrating creative solutions
and unique applications through complete projects, practical
tutorials, and useful design techniques.

MAKING THE NUMBERS WORK FOR YOU

by George Martin

Start ý Stating Our Case ý Working the Wiring ý A Case Study in Timer Interrupts ý Sources and PDF

STATING THE CASE

For the first example of unsigned number use, letýs work with the following assumptions. You have a 12-bit A/D converter that is measuring a real-world parameter that is always positive, such as oil pressure in an engine. The signal conditioning electronics produce a voltage ranging from 0 to 5 V for a given input range of oil pressure, say 0 to 100 psi. Inputting the 12-bit A/D into a 16-bit CPU is straightforward. The least significant bit of the A/D would be placed in the least significant bit on the CPU data bus, like this:

Bits 12ý15 would be read in as all zeros. So, 0-psi pressure would be 0 counts, and 100-psi pressure would be 4095 counts. Any manipulation of the data, such as filtering, would be a pure mathematical process on the binary readings.

PREVIOUS • NEXT