The Microcontroller Idea Book - Jan Axelson's Lakeview Research

10 REM use single-ended mode
20 REM set A to address of ADC
30 A=0C000H
40 FOR I=1 TO 8
50 XBY(A)=8+I-1
60 PRINT “Channel ”,I," = “, : PH0. XBY(A)
70 NEXT I
80 END
Writing to the converter causes the conversion to begin automatically. When the conversion
is complete, a read operation to the converter’s address causes the the converted value to
appear at DB0-DB7, where the 8052-BASIC reads it.
The INTR pin indicates when a conversion is complete, and can be used to trigger a read
operation. INTR is low when a conversion has occurred that has not yet been read. It goes
high after a read and remains high until the next conversion is completed. BASIC-52 is slow
enough that you don’t have to worry about waiting the maximum 60 microseconds between
requesting a conversion and reading the result, so you can ignore INTR and read the result
any time after a write.
Packaging Options
The ADC0848 comes in a 24-pin “skinny” DIP, with the pin rows spaced 0.3" apart as on
a 14-pin DIP. Sockets of this size, especially wire-wrap, can be hard to find, but in a pinch
you can place a 16-pin and 8-pin socket end to end. If you need only four analog inputs, use
the ADC0844, in a 20-pin skinny DIP.
Sensor Examples
Now let’s look a couple of examples of sensors that you can connect to the ADC0848.
Temperature
Using Sensors to Detect and Measure
Listing 9-2. Displays measurements of channels 1 through 8 on the
ADC0848.
The first is an LM34 temperature sensor. Unlike many other temperature sensors, the LM34
requires no calibration. Its output is a simple 10 millivolts per degree Fahrenheit. As Figure
9-6 shows, it’s available in several versions. The ones with a narrower range or lower
resolution are cheaper. If you prefer Celsius readings, use the LM35.
Figure 9-7 shows how to use an LM385-2.5 voltage reference to set the ADC’s VREF to 2.5V.
The converter then can measure temperatures from 0 to 250 degrees, and each bit in the
ADC0848’s output represents a 9.8 millivolt change in the sensor’s output.
The Microcontroller Idea Book 163