titus-larsen-titus-1981-apple-interfacing

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49318 WR TO SN7474 PIN 1 Fig. 6-22. Simple flag-clearing circuit schematic. flop, be sure that you remove the wire that was used to connect·+ volts to pin 1 on the SN7474 HiJ flop. The circuit shown in Fig. 6-22 will allow you to clear the flip-Ho with a POKE 49318 command. Modify your program so that line 65 is added: 65 POKE 49318,0 When this command is executed, the flag will be cleared. Since yo . may not know the state of the flag when you start the program, you might want to add a flag-clearing command at the start of the program, too. Now run the program. When the flag is detected, the Ha is immediately cleared. Then th count is incremented and dis played. . One of the benefits of using this type of flag, and using the assem bly-language subroutine to check the flag, is that you do not "staff the computer waiting for a flag, unless you want to. Thus, you ca write a program to check for a flag. If the flag is not present, th computer goes about some other task. If the flag is set, the device associated with it is serviced, and the computer then goes on. The BASIC interpreter in the Apple has a flag-checking command called WAIT. This command may be used to test for a flag, but if the flag is not found, the program continues to wai t for it, and it cannot do anything else. If a program "hangs up" waiting for a flag that never occurs, you must press the RESET key to re-establish control of the Apple. We refer you to Basic Programming Reference Manual for the Apple for more information about the WAIT com" mand. This command does not incorporate any flag-clearing commands. Purpose EXPERIMENT NO. 16 A SIMPLE ANALOG-TO-DIGITAL CONVERTER In this experiment, you will interface an 8-bit analog-to-digital converter to the computer. Several different types of measurements will be made. Discussion There are many applications for analog-to-digital converters, or AID converters in computer systems. The A/D converters allow the 154
· computer to measure analog voltages such as.those that would arise various signal sources and transducers. In this experiment, a 8-bit A/D converter will be used. The converter is a National ::ie1,1w0vi.1u'U'-'''u1 ADC0804-type converter. This converter has threeoutputs, so it can be interfaced directly to a microcomputer bus without difficulty. However, the three-state outputs have access time that can be as long as 200 nanoseconds. Thus, if you . attempt to use the ADC0804 A/D converter on your interface breadboard, you will find that the additional time required to actuate the bus interlocking circuitry to turn the data bus around for input will be too long. The data from the converter will be "missed" by the In order to perform this experiment, you must have access to the Apple data bus. This is explained in the following steps. Pin C@il'lfigurati@n of he Integrated Cirtl!Jit (fig. 6·23) ADC080X Duail-hi·Une P;;,clrnge .,_2:!. !'iii
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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
Page 105 and 106: 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: Yes. Simply reverse the commands at
Page 159 and 160: he minimum value should be in the r
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 (
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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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