titus-larsen-titus-1981-apple-interfacing

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+5 TO APPLE DATA BUS D7 ---" l ""'l l 12 r-l .,,. 0.1 13 D7 20 ADC0804 19 lOK ,__,,- 1-i 4 150pF 14 ANALOG INPUT 15 \ 20K OR V 1N + r----e----< 16 !OK 17 -,,,- +5V lK D0 --18'-1 DO +5 49319 cs lK WR WR 9 VREF/2 1--- RD Ri'i N/C INTR lK lK do not make proper contact with the 8216 chips when they are inserted into their respective sockets. Step 3 Enter the following program into your computer and run it: 10 POKE 49319,0 20 FOR T = 0 TO 100: NEXT T 30 PRINT PEEK(49319) 40 GOTO 10 What does the program do What is displayed on the video screen The program exercises the A/D converter, starting a conversion, providing a time delay so that the conversion can be performed, and then reading and displaying the data. Slowly adjust the potentiometer as you observe the data to confirm that the converter is operating. As you change the voltage setting of the potentiometer, you should see a corresponding change in the value displayed by the Apple. What is the minimum value What is the maximum value Does this seem to be what you would expect
he minimum value should be in the range of 0 or 1. The maximum alue should be between 253 and 255. This is what is expected from n 8-bit device, since it can only generate values between 0 and 255. tep 4 The ADC0804 chip has a Hag output that can be used to monitor e status of the converter; that is, busy or ready. This output is a gic zero when data is ready for the computer, and it is a logic one hen the converter is performing a conversion. This output is really e output of a flag circuit, and the flag is reset when the eight data its are read into the computer. Since the converter can perform any thousands of conversions in a second, is there any need to onitor this Hag signal robably not, since the converter will complete the conversion pross before the data can be accessed by a BASIC-language program. Can you suggest some possible uses for the Hag output e flag could be used for assembly-language A/D converter proamming. In assembly-language programs, ,the flag could be tested s an input to an input port, or it could be ' used with the interrupt on the 6502 microprocessor chip. Since thesei.are high-speed. applications, it would be useful to monitor the flag ;to determine when the converter had finished a conversion. Remove line 20 from your program and run the program. What do OU find The data values are the same as those observed when the program was used with the time delay steps. Thus, the converter is "outrun ·ng" the BASIC control program. ' The values displayed on the screen do not represent the actual voltage that is being measured, but are an 8-bit binary representa- 157
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lJ. 21862 APPLE® INTERFACING JONAT
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APPLE® INTERFACING by Jonathan A.
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Preface The purpose in writing this
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make no attempt to provide much det
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Contents CHAPTER 1 6502 PROCESSOR 9
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CHAPTER 1 6502 Processor The Apple
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Fig. 1- 1. 6502 Microprocessor chip
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locate the memory "cell" that is to
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IR.,view At this point, you should
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Gei'!eral-fi!Jrp@S('; I/ 0 Commaru:
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of an examined memory location. Fro
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will now explore the actions that e
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transfers will require more than ei
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grams are probably easier to write
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·when the Apple computer is progrn
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Y@bie ::!1. VNth i
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DECODED OUTPUT puter systems, the R
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1 1 1 Using Decoders In many cases,
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used in PEEK commands, for example
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An alternate approach is to use bot
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sections, but the address inputs, A
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fUNCTlON TABLES COMPARING CASCADING
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flexible decoding scheme, as shown
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until the power is turned off. Ther
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the logic zero state. In most cases
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ue in sequence (in binary), 255, 25
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DATA BUS DATA A SN74125 DATA B DATA
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R gates that control the enabling o
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state of the unused bits cannot be
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CHAPTER 4 Flags and Decisions n alm
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VALUE 00111010 00011010 11110000 00
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•• Addrss Byte Da;a Syie Mexacl
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INPUT DEVICE RD 49321 - READY/BUSY
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INPUT DEVICE INPUT PORT Dl Dl ' D3
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y-language programming will also be
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CHAPTER 5 Breadboarding 01 With the
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5 IN4001 (4) 6 ,.___'-'' N:...J LM3
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A15 AIO A13 Al2 Al4 All A9 AfJ D .L
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In the memory address mode, must pl
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PIN CONFIGURATION DJ, LOGIC DIAGRAM
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The actual ORing of these control s
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Fig. 5·10. Packaged version of the
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SIGNAL APPLE PfN INTERFACE PIN +12V
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·.chips have rather slow access ti
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are possible, we think that one exp
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in most of the experiments unless o
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tep 3 You may wish to test other po
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,..,,.,....,"'"' in the block from
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None of the outputs should be activ
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---" 2 CLR 20 2 CK Si\17474 The dev
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entered and run, It first asks you
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+5 Gl\ID LOGIC SWITCHES A B c D 16
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PR INT "O"; GOTO 65 If you wish to
Page 107 and 108: am, and the two-byte decimal calcul
Page 109 and 110: for each value that is input to the
Page 111 and 112: of the monitor screen each time the
Page 113 and 114: A = 128 420 B = PEEK(493 l 9) 430 F
Page 115 and 116: il!!lie -2. 0 THEN . . .
Page 117 and 118: program. You may forgotten steps to
Page 119 and 120: The A output, RD 49319, has already
Page 121 and 122: used the following program: FOR A =
Page 123 and 124: · numbers would have to be "split"
Page 125 and 126: tep 1 The input port and output por
Page 127 and 128: 0'"""c"y'·i- the relative values t
Page 129 and 130: and output ports are simply additio
Page 131 and 132: e has been divided into 256 values,
Page 133 and 134: e converter will not burn out, sinc
Page 135 and 136: 07 DATA BUS DO 3 4 7 a 13 14 17 18
Page 137 and 138: each decade. The bed code is used i
Page 139 and 140: LED BIT RED } D3 YELLOW EL M D4 GRE
Page 141 and 142: : : FOR T = 0 TO 770 NEX T T NEX T
Page 143 and 144: Thus, by testing the value input fr
Page 145 and 146: he six LEDs should be removed from
Page 147 and 148: Yo'1 should be able to develop the
Page 149 and 150: INPUT "LAST TWO DIGITS ";A$ IF A$ =
Page 151 and 152: tfhe program first tests the reset
Page 153 and 154: would you program the computer so t
Page 155 and 156: Yes. Simply reverse the commands at
Page 157: · computer to measure analog volta
Page 161 and 162: 130 Y2 = PEEK(49319)/ 1.594 140 HPL
Page 163 and 164: You probably will not see much chan
Page 165 and 166: D7 D6 D5 D4 D3 D2 Dl DO 'b- • "A"
Page 167 and 168: ll'i!i Name 1 1/0 SELECT 2- 17 A 15
Page 169 and 170: ADDRESS BUS A7-AO :> MEMORY 256 x 8
Page 171 and 172: !n!erfac" Slel Addwess lta"%Je 0 C0
Page 173 and 174: 28 INT IN SLOT 6 +5 lK Lr LOCAL INT
Page 175 and 176: USER 1 This input will allow you to
Page 177 and 178: puts. You must be careful in your d
Page 179 and 180: CONTROL/ DATA input at pin 12 ( C/D
Page 181 and 182: 93427 OR EQUIV ROM ADDRESS BUS 1---
Page 183 and 184: use of red LEDs is recommended, sin
Page 185 and 186: APPENDIX B Parts Required for the E
Page 187 and 188: APPENDIX 6502 Microprocessor Techni
Page 189 and 190: MC§f.500 IE1lriy {D"i) This input
Page 191 and 192: MCS6500 INSTilUCTION SH-ALPHABETICA
Page 193 and 194: ,, ,, T!M!NG Il-01! READING DI\ TA
Page 195 and 196: MCS0t-20 PWH¢01 ns PWH¢2 ¢11ou11
Page 197 and 198: APPENDIX D Apple Interface Breadboa
Page 199 and 200: APPENDIX E Printed-Circuit Board Ar
Page 201 and 202: !'i9. E-2. Printecl-
Page 203: F t • I +: a... :::> 0 a: (!> 0 (
Page 206 and 207: Controllers, 14 Converter analog-to
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Pin configuration-cont SN7474, 150
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The Blacksburg Group According to B
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