titus-larsen-titus-1981-apple-interfacing

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If this type of a "polled" interrupt is used, with the computer polling each of the devices that could have generated an interrupt, a priority can be established in the software. Thus, if the computer checks the devices in the order A, B, C, and so on, device A has the highest priority, since it will be checked first when an interrupt is detected. The interface slots also have two other interrupt lines that may be of interest, depending upon your application. These signals are the interrupt input (INT IN) at pin 28, and the interrupt output (INT OUT) at pin 23. These signals are used to "daisy chain" interrupt signals form one card to the next. The signals are only connected between the interface connectors, as shown in Fig. 7-6. Thus, the INT OUT signal on slot 1 is connected to the INT IN signal on slot 2, the INT OUT on slot 2 is connected to the INT IN on slot 3, and so on. The INT IN and IN OUT lines are only connected to the adjacent interface slot, and they do not go any further. REAR OF APPLE 0 23 28 23 23 28 INT OUT INT IN *NOTATIONS ARE INTERCHANGEABLE, DEPENDING UPON USE. A simple daisy-chained interrupt scheme is shown in Fig. 7-7, The lower-priority interrupting devices are further down the chain, further from the INT connection to the 6502 microprocessor chip. In this circuit, a higher priority device can pass its interrupt request up the chain, blocking any interrupt requests from the lower priority devices that are further down the chain. Once the higher-priority device has been serviced and its interrupt flag has been cleared, it will "open" its gate and allow the lower priority interrupt request to pass on to the computeL As you can see, the computer still needs some way of determining which device is generating the interrupt, so that it can select the corresponding service subroutine. This type of
28 INT IN SLOT 6 +5 lK Lr LOCAL INTERRUPT HIGHEST PRIORITY TO IRQ PIN 30 ... .p· > =- 1" :I" .. ;· .. a. a· .. ::: c "! .. .a· :I !.. " 0 :I :a la i. SLOT 3 +5 lK INT IN 28 ---
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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
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am, and the two-byte decimal calcul
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for each value that is input to the
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of the monitor screen each time the
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A = 128 420 B = PEEK(493 l 9) 430 F
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il!!lie -2. 0 THEN . . .
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program. You may forgotten steps to
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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 and 158: · computer to measure analog volta
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: !n!erfac" Slel Addwess lta"%Je 0 C0
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
Page 208: Pin configuration-cont SN7474, 150
Page 211: The Blacksburg Group According to B
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