The Microcontroller Idea Book - Jan Axelson's Lakeview Research

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Chapter 9 Figure 9-8. VOUT varies with the light intensity, and output current, of the solar cell. from 0 in darkness to 300 milliamperes in full sun. The voltage across the cell is about 0.5 volt. An LF353 dual op amp converts the solar cell’s current into a voltage that the ADC0848 can measure. Most of the solar cell’s current flows through the 1-ohm resistor to ground. Since the solar cell’s voltage is only about 0.5 volt, the power dissipated by the 1-ohm resistor is only about 0.15 watt in full sun. About one percent of the solar cell’s output flows through the 100-ohm resistor. This same current flows through the 1.6K resistor, with the result that the voltage at pin 1 of the LF353 varies from 0 to about -4.75V. This voltage is proportional to the intensity of the light hitting the solar cell. The second op amp is an inverter that converts the voltage to positive levels that the ADC0848 can measure. Listing 9-4 assumes that pin 7 of the LF353 connects to Channel 8 of the ADC0848. On request, the program converts the analog input and displays the result. 166 The Microcontroller Idea Book
Using Sensors to Detect and Measure Listing 9-4. Measures and displays solar energy detected by solar-cell circuits at Channel 8 of ADC0848. 10 REM set A to address of ADC 20 A=0C000H 30 REM set C to channel to read (1-8) 40 C=8 50 REM use single-ended mode, select channel, start convert 60 XBY(A)=8+C-1 70 REM FS=full-scale voltage (5V)/full-sun output (4.75V) 80 FS=1.05 90 B=XBY(A) 100 T=INT(FS*B*100/255+.5) 110 PRINT “Solar energy = ”,T," percent of full sun" 120 PRINT “press any key to take another measurement” 130 D=GET : IF D=0 THEN GOTO 130 140 GOTO 60 150 END Level Translating As you can see, not every sensor has an output that can connect directly to the ADC0848’s inputs. A sensor’s output may vary from -2 to -1V, from -0.5 to +0.5V, or from -12 to +12V. In all of these cases, you need to shift the signal levels and sometimes adjust the signal range to be compatible with a converter that requires inputs between 0 and 5 volts. Figure 9-9 shows a general-purpose circuit that can amplify or reduce input levels, and can also raise or lower the entire signal by adding or subtracting a voltage. Separate, independent adjustments control the gain and offset. The circuit is a series of three op amps: a buffer, a level shifter, and an amplifier. The example circuit uses three of the devices in an LF347 quad JFET-input op amp. The LF347 has fast response and high input impedance. You may use a different op amp if you prefer. The first op amp is a noninverting amplifier whose output at pin 1 equals VIN. The op amp presents a high-impedance input to VIN, to minimize loading effects. The second op amp is an inverting summing amplifier that shifts pin 1’s voltage up or down as R5 is adjusted. Adjusting R5 raises and lowers the voltage at pin 7, but the signal’s shape and peak-to-peak amplitude remain constant. The third op amp is an inverting amplifier whose gain is adjusted by R4. This amplifier increases or decreases the peak-to-peak amplitude of its input. The Microcontroller Idea Book 167
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The Microcontroller Idea Book Circu
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Table of Contents Chapter 1 Microco
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Chapter 11 Control Circuits 185 Swi
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Introduction Introduction This book
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A chapter on assembly-language inte
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Microcontroller Basics 1 Microcontr
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But along with cheap, powerful, and
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makes sense. For simpler designs, a
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Microcontroller Basics Several tech
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Interpreters and compilers are two
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Inside the 8052-BASIC 2 Inside the
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Inside the 8052-BASIC • You can a
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hardware manuals. For programming,
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Inside the 8052-BASIC Figure 2-2 Pi
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Inside the 8052-BASIC Table 2-2. (p
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Inside the 8052-BASIC Code and data
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Powering Up 3 Powering Up This chap
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Powering Up Table 3-1. Parts list f
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Powering Up Figure 3-2. Truth table
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Powering Up Jumper J3 chooses the c
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Powering Up Figure 3-3. This is the
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Powering Up Construction Tips These
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Powering Up Serial Connectors Conne
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You’re now ready to power up the
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Powering Up PRINT XTAL Line Editing
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Powering Up PORT 1 Bit Values: Bit
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Powering Up Listing 3-3. Allows use
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10 CLOCK 1:TIME=0:SEC=0 20 A=0 30 P
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Saving Programs 4 Saving Programs I
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guaranteed for at least ten years.
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Saving Programs Figure 4-3. Circuit
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Jumper J4 is optional. It enables y
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memory on bootup. This is what allo
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This is the recommended algorithm f
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Saving Programs Figure 4-5. Additio
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problems with EPROMs that have a 10
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supply. The chip requires an additi
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Programming 5 Programming When you
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Subroutines have two advantages. Fi
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Programming • Hexadecimal numbers
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Programming It can be hard to find
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Programming Math Operators = + - *
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Programming expression / expression
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Programming DO: [program statements
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Programming LOG(expression) Returns
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Programming PH0.@ Same as PRINT@, b
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Programming RCAP2 Retrieves or assi
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Programming PRINT TAB(2) “hello
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Inputs and Outputs 6 Inputs and Out
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Unassigned space remains in the mem
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U11 is a 74HCT138 3-to-8-line decod
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If you wish, you can wire U14’s i
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Inputs and Outputs Figure 6-4. Outp
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Inputs and Outputs Listing 6-2. Set
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The 82C55 also has CMOS-compatible
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Inputs and Outputs Pin Symbol Input
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Inputs and Outputs An 8255 Interfac
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Inputs and Outputs XBY(0FC03h)=9BH
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To set or clear a different bit, de
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Switches and Keypads 7 Switches and
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Switches and Keypads Figure 7-2. Us
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exact value depending on the switch
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Page 127 and 128: Switches and Keypads Figure 7-6. A
Page 129 and 130: Switches and Keypads Custom Keypads
Page 131 and 132: Switches and Keypads • A single c
Page 133 and 134: Switches and Keypads Listing 7-3. T
Page 135 and 136: Displays 8 Displays In addition to
Page 137 and 138: Displays Figure 8-1. LED interfaces
Page 139 and 140: Displays Figure 8-2. Ways to connec
Page 141 and 142: Displays Figure 8-4. Four output po
Page 143 and 144: Displays Figure 8-5. The ICM7218D c
Page 145 and 146: In Figure 8-5’s circuit, an 82(C)
Page 147 and 148: Displays Figure 8-7. With the TC721
Page 149 and 150: Displays Figure 8-8. With a charact
Page 151 and 152: Table 8-1. LCD modules containing t
Page 153 and 154: Each character in the CG ROM and CG
Page 155 and 156: Displays Interfacing Full control o
Page 157 and 158: Displays Listing 8-4 (page 2 0f 2).
Page 159 and 160: Displays Listing 8-5. Displays key
Page 161 and 162: Displays Listing 8-6 (page 2 of 2).
Page 163 and 164: Using Sensors to Detect and Measure
Page 165 and 166: • What power supplies are availab
Page 171 and 172: different ground symbols for the tw
Page 173 and 174: 10 REM use single-ended mode 20 REM
Page 175: Using Sensors to Detect and Measure
Page 181 and 182: Clocks and Calendars 10 Clocks and
Page 183 and 184: Listing 10-1. Uses BASIC-52’s rea
Page 185 and 186: Clocks and Calendars Figure 10-1. P
Page 187 and 188: Clocks and Calendars Table 10-1. Re
Page 189 and 190: If you want an alarm frequency othe
Page 191 and 192: Clocks and Calendars Listing 10-3 (
Page 193 and 194: Clocks and Calendars Listing 10-3 (
Page 195 and 196: Control Circuits 11 Control Circuit
Page 197 and 198: the LSTTL part, and wire the desire
Page 199 and 200: Control Circuits Listing 11-1. Cont
Page 201 and 202: Control Circuits Listing 11-2. Demo
Page 203 and 204: Control Circuits disables the outpu
Page 209 and 210: Wireless Links 12 Wireless Links Wi
Page 211 and 212: Wireless Links Figure 12-2. This in
Page 213 and 214: Wireless Links Because there are th
Page 215 and 216: Wireless Links Figure 12-4. The GP1
Page 217 and 218: through the LEDs. If you prefer an
Page 219 and 220: Wireless Links Figure 12-6. Using a
Page 221 and 222: Wireless Links Figure 12-7. Using a
Page 223 and 224: Wireless Links IREDs emit energy at
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Calling Assembly-language Routines
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into memory in the 8052-BASIC syste
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2048h in code memory. This is becau
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Binary value 1100 0101 Hex equivale
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Successful assembly is a good sign,
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statement must match the address in
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• BASIC-52’s ON EX1 instruction
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Running BASIC-52 from External Memo
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14-1 for longer delays between writ
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In Figure 3-1, tie pin 31 of U2 (EA
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Related Products 15 Related Product
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Finally, a compiled BASIC program u
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Related Products Figure 15-3. Blue
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Sources Appendix A Sources This App
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Programming and Interfacing the 805
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Sources Product Vendors The followi
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Sources Electronics 123 17921 Rowla
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Sources Micro Future 40944 Cascado
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Sources Siemens Components 2191 Lau
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Programs for Loading Files Appendix
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Programs for Loading Files Listing
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Number Systems Appendix C Number Sy
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Number Systems This table shows the
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Index Index A ADC, 158 - 169 addres
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Index S sample and hold, 169 SBC, 3
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The Microcontroller Idea Book - Jan Axelson's Lakeview Research

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