The Microcontroller Idea Book - Jan Axelson's Lakeview Research

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Chapter 8 Figure 8-9. Using an 8255 to control a character-based LCD module. Read operations are similar to writes, with R/W high instead of low. The data appears on D0-D7 in 320 nanoseconds or less after E goes high. The HD44780 cannot accept a new instruction until it has finished executing its previous instruction. Table 8-2 shows the maximum time each instruction requires. BASIC-52 is slow enough that you don’t have to worry about the required delays. If you’re using an assembly-language routine, your program must include delays after each instruction, or you can use the instruction that reads the HD44780’s busy flag at D7 to determine when the module is ready to accept a new instruction. 144 The Microcontroller Idea Book
Displays Interfacing Full control of an LCD module requires 8 bidirectional lines for reading and writing data and 3 outputs for the control signals. To save four lines, you can use the 4-bit data interface described later. Also, the ability to read the display and the busy flag at D7 are optional. If you give these up, you can use outputs (such as the 74HC374’s) instead of bidirectional port bits for D0-D7, and eliminate one of the control lines by tying R/W low. Figure 8-9 shows an LCD module connected to an 82(C)55, using an 8-bit bidirectional interface. The interface uses Port A and three bits of Port C on an 8255. You can use any of the 8255’s port bits, if you write your program to match. On the LCD module, pins 1-3 connect to ground, +5V, and a contrast potentiometer. For maximum contrast, connect pin 3 directly to ground. Pins 4-6 are the control signals for the LCD module. These connect to three outputs on Port C. The eight data bits, pins 7-14 on the LCD module, connect to Port A. Listing 8-4 is a BASIC-52 program that initializes a 2-line display and writes LINE 1 and LINE 2 to the matching lines. Initializing the module. On power up, the LCD module must initialize properly. If power-up is clean, with the supply voltage rising from 0.2V to 4.5V in 10 milliseconds or less, the module initializes automatically. But, if power-up doesn’t meet this requirement, your program has to provide the initialization routine. It’s a good idea to always include an initialization routine in your program, since it does no harm, and if the module doesn’t initialize properly, it won’t respond correctly or at all. Table 8-3 summarizes the initialization procedure. In short, the module must first receive three identical commands selecting an 8-bit interface. BASIC-52 easily provides the necessary delays between the commands. To begin the initializing, you must send the instruction to select an 8-bit interface, even if your interface is four bits. Once this is done, the instructions for Function Set, Display On, Display Clear, and Entry Mode Set tell the controller the configuration you desire. The automatic power-on initialization routine turns the display off, so if you use it, you have to turn the display on by writing 0Ch to the instruction register. When initializing is complete, you can control the display as you wish, though you can’t change the number of display lines unless you reinitialize from the beginning. Listing 8-4 has two subroutines, one for writing characters to the display and one for writing instructions. To write a character, set D equal to the character’s code, and call subroutine 800, which sets RS, writes the character to the display, and toggles E. To write an instruction, The Microcontroller Idea Book 145
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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
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 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: Each character in the CG ROM and CG
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 (
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
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Control Circuits Listing 11-4. Cont
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Control Circuits Listing 11-5. Cont
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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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