The Microcontroller Idea Book - Jan Axelson's Lakeview Research

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Chapter 6 90 The Microcontroller Idea Book
U11 is a 74HCT138 3-to-8-line decoder that generates individual chip-enable signals for eight 1K blocks in the memory area from E000h to FFFFh. It works the same way that U6 generates chip selects for 8K blocks in the main circuit. U11 is enabled whenever pin 7 of U6 is low, which occurs when the 8052-BASIC reads or writes to addresses from E000h to FFFFh. Address lines A10, A11, and A12 determine which of U11’s outputs goes low when the chip is enabled. As with U6, each output is low for a different memory area. For example, pin 15 is low only when addresses from E000h to E3FFh are being read or written to. One possible point of confusion is that both pin 7 of U6 ( in Figure 3-1) and pin 15 of U11 are chip-selects with a starting address of E000h. One controls memory accesses in the entire 8K block from E000h to FFFFh, while the other controls only the 1K block from E000h to E3FFh. To distinguish the two, I’ve labeled U11’s pin 15 as E000H-1K. U12 and U14 are examples of input and output ports that U11 can enable. An Input Port Inputs and Outputs U12 is a 74LS244 octal buffer that adds eight inputs to the circuit. The buffer’s Y outputs connect to the system’s data bus (D0-D7). The chip has two groups of four buffers, with each having its own enable input (1G and 2G). For this application, the enables are tied together, and all eight buffers are accessed as a group. I used an LSTTL device for the buffer rather than a CMOS 74HC244 for a couple of reasons. The LSTTL chip has Schmitt-trigger inputs, which are less sensitive to noise. Plus, unlike CMOS, the LSTTL buffer requires no pull-up resistors at unused inputs. OR gate U9B ensures that U12 is enabled only when U2 (the 8052-BASIC chip) reads an address from E000h to E3FFh. When this occurs, output-enable pins 1 and 19 go low, the buffer’s outputs follow its inputs, and U2 reads the data that U12 has placed on D0-D7. After a read operation, pins 1 and 19 go high and U12’s outputs are high-impedance. In other words, the outputs are electrically similar to an open circuit, which ensures that they won’t interfere with other operations on the data bus. In the circuit, U12 is read-only. Write operations to E000h have no effect. To access U12 at a different address, wire pin 4 of U9B to a different output of U11. Memory decoding options. Note that although U12 holds just one byte of information to read, you can access it at any address from E000h to E3FFh. This may seem like a waste of The Microcontroller Idea Book 91
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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
Page 49 and 50: Powering Up PRINT XTAL Line Editing
Page 51 and 52: Powering Up PORT 1 Bit Values: Bit
Page 53 and 54: Powering Up Listing 3-3. Allows use
Page 55 and 56: 10 CLOCK 1:TIME=0:SEC=0 20 A=0 30 P
Page 57 and 58: Saving Programs 4 Saving Programs I
Page 59 and 60: guaranteed for at least ten years.
Page 61 and 62: Saving Programs Figure 4-3. Circuit
Page 63 and 64: Jumper J4 is optional. It enables y
Page 65 and 66: memory on bootup. This is what allo
Page 67 and 68: This is the recommended algorithm f
Page 69 and 70: Saving Programs Figure 4-5. Additio
Page 71 and 72: problems with EPROMs that have a 10
Page 73 and 74: supply. The chip requires an additi
Page 75 and 76: Programming 5 Programming When you
Page 77 and 78: Subroutines have two advantages. Fi
Page 79 and 80: Programming • Hexadecimal numbers
Page 81 and 82: Programming It can be hard to find
Page 83 and 84: Programming Math Operators = + - *
Page 85 and 86: Programming expression / expression
Page 87 and 88: Programming DO: [program statements
Page 89 and 90: Programming LOG(expression) Returns
Page 91 and 92: 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: Unassigned space remains in the mem
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
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Table 8-1. LCD modules containing t
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Each character in the CG ROM and CG
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Displays Interfacing Full control o
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Displays Listing 8-4 (page 2 0f 2).
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Displays Listing 8-5. Displays key
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Displays Listing 8-6 (page 2 of 2).
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Using Sensors to Detect and Measure
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• What power supplies are availab
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different ground symbols for the tw
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10 REM use single-ended mode 20 REM
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Clocks and Calendars 10 Clocks and
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Listing 10-1. Uses BASIC-52’s rea
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Clocks and Calendars Figure 10-1. P
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Clocks and Calendars Table 10-1. Re
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If you want an alarm frequency othe
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Clocks and Calendars Listing 10-3 (
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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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