The Microcontroller Idea Book - Jan Axelson's Lakeview Research

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Chapter 8 Listing 8-3. Controls eight 7-segment LEDs with ICM7218 driver. 10 REM address of 8255 Port A 20 A=0FC00H 30 REM address of 8255 control word 40 X=A+3 50 REM set 8255 for all outputs 60 XBY(X)=80H 70 REM set WR 80 XBY(X)=9 90 REM write to each digit 100 FOR M=0 TO 7 110 REM step through all numbers at each digit 120 FOR I=0 TO 8 130 REM add 10h to turn off decimal point 140 D=I+10H+M*20H 150 GOSUB 500 160 REM delay to display each digit 170 K=500 180 FOR J=1 TO K : NEXT J 190 NEXT I 200 NEXT M 210 END 490 REM write data to port A and toggle W (PC.4) 500 XBY(A)=D 510 XBY(X)=8H 520 XBY(X)=9 530 RETURN range for peak current for most LEDs, and the 2.5-milliampere average current causes the displays to appear brighter than you might expect. With all digits displaying 8’s, this circuit draws 140 milliamperes, so be sure your power supply can handle it. To write a value to the display, you select the digit with data-address inputs DA0-DA2, write the data to inputs ID0-ID7, and strobe WRITE low. The WRITE pulse must be at least 400 nanoseconds wide, and ID0-ID7 must remain valid for at least 125 nanoseconds after WRITE goes high. BASIC-52 is slow enough to meet these requirements, using XBY statements to write to the port that controls the 7218C. Pin 9 allows you to select one of three modes, which determine what digits the displays show. In Code B mode, you can display the message HELP. 134 The Microcontroller Idea Book
In Figure 8-5’s circuit, an 82(C)55 controls the 7218C. For complete control, the circuit requires 10 outputs. Bits 0-4 of Port A determine the data to be written, including a decimal point controlled by ID7. If you don’t need the decimal point, tie pin 7 of the 7218C low. Bits 5-7 of Port A select the digit to write to. If you have four or fewer displays, you can tie one or more of these lines low and free up another port bit. Port C, bit 4 controls WRITE. The display-mode input is tied high to select hexadecimal mode. If you instead tie pin 9 to a port bit, you can turn off the display by bringing the bit low. To allow selecting different modes, connect an additional output bit to the 7218D’s MODE input. Listing 8-3 uses the 7218D to display data, using Figure 8-5’s circuit. 7-segment LCDs Displays An alternative to LEDs is liquid-crystal displays (LCDs). Unlike LEDs, which consume several milliamperes per segment, LCDs are voltage-controlled and require very little operating current. Compared to LEDs, LCDs are easy to read in bright light. However, because LCDs don’t emit light as LEDs do, but merely absorb or transmit it, you need additional lighting to see them in the dark. LCDs also tend to have narrower viewing angles than LEDs. So, whether to use LEDs or LCDs may depend on where and how you will use the display. Most 7-segment LCD modules contain two or more digits. Like the LEDs, a 7-segment LCD creates a numeral by turning on selected segments. Each LCD segment contains a thin layer of liquid crystal between two layers of glass. Liquid crystals are organic compounds that act as electrically controlled light polarizers. In a positive-image display (the most common type), applying a voltage across a segment causes the segment to appear dark, or opaque, while removing the voltage causes the segment to appear light-colored, or transparent. Negative-image displays are opaque when not powered, and transparent when powered. By applying and removing voltages across individual segments, you can display numeric, alphabetic, and other characters. Applying a constant voltage to an LCD segment will eventually destroy it. Instead, you must drive the segment with an alternating voltage, typically a square wave that alternately applies +5 and -5V across the segment. Single-digit driver. Figure 8-6 shows an LCD module driven by a 4543B LCD latch/decoder/driver. The 4543 is a lot like the 4511 LED driver, with the addition of a phase input that accepts a square wave for driving the segments. A typical drive frequency is around 100 Hertz. A 555 timer provides the phase input, or you can use any oscillator output. The Microcontroller Idea Book 135
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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
Page 93 and 94: Programming RCAP2 Retrieves or assi
Page 95 and 96: Programming PRINT TAB(2) “hello
Page 97 and 98: Inputs and Outputs 6 Inputs and Out
Page 99 and 100: Unassigned space remains in the mem
Page 101 and 102: U11 is a 74HCT138 3-to-8-line decod
Page 103 and 104: If you wish, you can wire U14’s i
Page 105 and 106: Inputs and Outputs Figure 6-4. Outp
Page 107 and 108: Inputs and Outputs Listing 6-2. Set
Page 109 and 110: The 82C55 also has CMOS-compatible
Page 111 and 112: Inputs and Outputs Pin Symbol Input
Page 113 and 114: Inputs and Outputs An 8255 Interfac
Page 115 and 116: Inputs and Outputs XBY(0FC03h)=9BH
Page 117 and 118: To set or clear a different bit, de
Page 119 and 120: Switches and Keypads 7 Switches and
Page 121 and 122: Switches and Keypads Figure 7-2. Us
Page 123 and 124: exact value depending on the switch
Page 125 and 126: Switches and Keypads Figure 7-4. Tw
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: Displays Figure 8-5. The ICM7218D 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 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 (
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Control Circuits 11 Control Circuit
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the LSTTL part, and wire the desire
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Control Circuits Listing 11-1. Cont
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Control Circuits Listing 11-2. Demo
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Control Circuits disables the outpu
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Wireless Links 12 Wireless Links Wi
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Wireless Links Figure 12-2. This in
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Wireless Links Because there are th
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Wireless Links Figure 12-4. The GP1
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through the LEDs. If you prefer an
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Wireless Links Figure 12-6. Using a
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Wireless Links Figure 12-7. Using a
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Wireless Links IREDs emit energy at
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In the infrared link, the amount of
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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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