The Microcontroller Idea Book - Jan Axelson's Lakeview Research

statement must match the address in your file’s org directive. A missing ret instruction in
the routine will also cause the system to crash.
Example: Creating a Sine Wave
When you have the simple routine working, you’re ready to move on to bigger things. For
the sine-wave project, we’ll begin by generating a sine wave entirely with BASIC-52
statements. This way, we can first test the added circuits as well as the algorithm, or sequence
of steps, that we plan to use to generate the sine wave. It also illustrates the speed limits of
BASIC-52.
The Circuits
Calling Assembly-language Routines
Figure 13-2 shows the circuit that interfaces to the 8052. I adapted the circuit from an
example in National Semiconductor’s data sheet for the DAC0832.
U1 is a DAC0832 digital-to-analog converter, or DAC, which converts data inputs D0-D7
into an analog voltage. D0-D7 are controlled by an output port at E400h. You may change
this address to match any output port on your system.
Listing 13-4. Sine-wave generator for Figure 13-2’s circuit.
10 REM Begins by calculating and storing sine values
20 REM for 256 locations along a sine wave.
30 REM Line 100 converts a position in the sine wave
40 REM (0-255) to the radians required by the sine
50 REM operator: (0.0246 = 2*PI/256). Adding 1 to the
60 REM sines makes all values positive, from 0 to +2.
70 REM Multiplying by 127.5 results in values that
80 REM range from 0 to 255.
90 FOR I=0 TO 255
100 XBY(3000H+I)=INT((SIN(I*.0246)+1)*127.5+.5)
110 NEXT I
120 PRINT “Sine values are stored in RAM (3000h-30FFh)”
130 PRINT “Press Control+C to quit”
140 REM Write the values in sequence to E400h
150 DO
160 FOR I=3000H TO 30FFH
170 XBY(0E400H)=XBY(I)
180 NEXT I
190 WHILE 1=1
200 END
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