28128 Parallax Inc, 28128 Datasheet - Page 62

• Manufacturer Part Number: 28128
• Description: KIT BASIC ANALOG/DIGI PARTS ONLY
• Manufacturer: Parallax Inc

Specifications of 28128

• Accessory Type: ADC, DAC
• Product: Microcontroller Accessories
• For Use With/related Products: BASIC Stamp® 2 and Board of Education
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Interpreting the Output
The ADC0831 measures an analog voltage at its input. Then it sends the BASIC Stamp a
binary number describing the value it measured. For now, we’ll focus on a voltage scale
that starts with 0 volts and ends at 5 volts.
With an 8-bit binary number, you can start counting with 00000000 and count all the way
up to 11111111. Translated to decimal numbers, it's the same as counting from 0 to 255.
When applied to a 5 volt scale that starts at 0 volts, it’s the same as counting from 0 to 5
volts using 255 voltage steps.
For the 5 volt scale, when the ADC0831 measures 0 volts, you get 00000000. When it
measures 5 volts, the output is 11111111. It turns out that the Debug Terminal output
10110100 from Figure 3-4 is the same as the decimal number 180. Decimal-180 in turn
corresponds to a measured voltage of 3.53 volts.
Binary to Decimal Conversion Revisited
So how do we know that 256 combinations can come from an 8-bit binary number?
Remember, you can always tell how many numbers (combinations of 0s and 1s) can
come from a given number of bits by using this formula from Chapter #2:
This means the number of combinations equals two raised to the power of the number of
bits. For 8-bits, the number of combinations is 2
combinations is 2
Let's use the two-step method from Chapter #2 to convert the 8-bit binary number
10100101 to its decimal equivalent. Here is a repeat of the bit multipliers table to work
with:
combinations =2
Bit
Multiplier
12
Table 3-1:Bit Multipliers for an 8-bit Binary Number
= 4096, and so on.
bits
128
7
64
6
32
5
16
8
4
= 256. For 12-bits, the number of
3
8
2
4
1
2
0
1