Behavior Research Methods & Instrumentation 1981, Vol. 13 (2),221-226 Low-cost microcomputer networking: How to get high throughput on a low budget ADAM V. REED Graduate Faculty ofSocial andPolitical Science NewSchoolforSocial Research. New York. New York 10011 DANIEL LEWART HolmdelHigh School. Holmdel. New Jersey 07733 and LINDA H. SCHNEIDER New York University. New York. New York 10003 A very low-cost, high-throughput laboratory data acquisition and experiment control.ysteDl may be configured by using a 8tar network architecture with a IOW-C08t microcomputer u network controller and one or more microprocessor-based single-board controllen a. satellites. A network of this type, using Apple II microcomputer (fl,600 with 48K RAM and one minidiskette drive) a8 main node and up to seven KIM-I microcontrollers (fl69 each) a8 satellites is described, and its development is discussed in detail. This paper describes the local network approach to the problem of increasing the throughput of laboratory computer systems. The main advantage of this approach is low cost. A rough rule of thumb used by system planners is that with the traditional single-processor approach, every doubling of throughput triples the cost of the system. With the network approach, each satellite processor adds about 10% to the cost of hardware for the system. With this kind of cost advantage, it is rather surprising that the network approach is not more widely used in experimental laboratories. One likely explanation for this is the mystique acquired by networking in the early days of computing. According to this mystique, network development requires sophisticated development systems and large amounts of professional effort. One of our goals for this paper is to show how outdated this mystique has become in the last couple of years. The microcomputer network described in the present paper was developed with the network controller, a standard integer-version Apple II microcomputer, as its own resident development system. The software development effort took a total of 10 h of the first author's time, as well as about 16 h of spare time contributed by the second author while he was a student at Holmdel High School. The hardware interface was built by the third author in slightly under 5 h. While a psychologist who is not also a computer engineer may have to add between $500 and $1,000 in consultants' fees to the cost of the network described in this paper, a microcomDaniel Lewart is now at the Massachusetts Institute of Technology. Copyright 1981 Psychonomic Society, Inc. puter network could still constitute the most costeffective approach to adequate system throughput. A computer network is a system of two or more independently programmable processors, at least one of which is capable of exerting complete control over all the others under the direction of its own program. Our design objectives were to provide adequate throughput for current experiments, to provide future expansion capability up to twice the maximum requirements of any single foreseeable experiment in cognitive psychology, and to minimize development time for the present system as well as for future experiments. Note that a capability for simultaneous execution of several experiments was not one of our design objectives. In general, the most cost-effective way of running several experiments is to run them on separate systems. HARDWARE The Central (Controller) Node The Apple II was originally chosen as a laboratory computer primarily because its all-socketed construction facilitated the hardware modifications (Reed, 1979) necessary for tachistoscopic stimulus presentation and accurate timing of stimulus-response latencies. Socketed construction also minimizes down time, since most malfunctions may be repaired on site by removing the malfunctioning integrated circuit (Ie) from its socket and plugging in a replacement. The Apple also meets both requirements for a central node in a local computer network. The first of these requirements is that the central node be equipped with digital input and output lines capable of communicating with satellite processors. 221 0005 -7878/81/020221-06$00.85/0 222 REED, LEWART, AND SCHNEIDER The other requirement is that the central node be usable as a development system for real-time routines being developed for implementation on the satellite processor. If real-time program development is being done in assembly language, this means that central node software must include a symbolic assembler capable of assembling code to an object (OBJ) location in random-access memory (RAM) other than the actual logical origin (ORG) the program is to have on the system on which it will be eventually executed. In general, any assembler having separate OBJ and ORG pseudooperations or assembler directives will be capable of doing the job. The assembler included in the Microproducts, Inc., development system package for the Apple II is equipped with these features, and it is this package that is currently used on the network to develop real-time software for the KIM-I. Unfortunately, assemblers seldom have the above features in the same package with interactive assembly capabilities necessary for network development. The networking software for the Apple II was actually developed without a symbolic assembler. We used the interactive miniassembler included in the firmware of the standard integer-version Apple II. The absence of symbolic labeling capability in this firmware was more than made up for by its interactive debugging and structuring features. The integer-version Apple II is equipped with a debugging monitor that has go (run), list (disassemble), trace, single step, register examine, and register fill commands, as well as multiple command sequence capability. Any debugging monitor command sequence may be executed without leaving the miniassembler. Moreover, the go command emulates a JSR subroutine call, a feature that encourages FORTH-like structured programming. An interactive assembler of this type facilitates the segmenting of code into short externally callable subroutines, each of which is fully debugged and tested at the time it is written, and before the programmer goes on to write the next segment. The Satellite Node(s) The microcomputer/microcontroller selected for the function of a satellite in a laboratory microcomputer network must satisfy four criteria. First, the instruction set of its processor should be the same as that of the central node's, a condition essential to uncomplicated cross-development of real-time software for experiments. Second, an external device, capable of being simulated by the central node processor, should be able to load desired information into the satellite's memory, to obtain a dump of the satellite's memory on demand, and to start program execution at any desired location in the satellite's memory. Our requirement of reducing development effort to the minimum added an extension of this condition: The software for all of the above functions had to be already present as firmware in the satellite's read-only memory (ROM). This would free us from having to write any real-time networking software for any microcomputer other than the central node, on which adequate development software was known to be available. The third and fourth conditions were the obvious ones: The satellite had to be able to perform the functions necessary to carry out its role in psychological experiments, and it had to fit our budget. The first of the above conditions narrowed consideration to microcomputers using the 6502 processor used in the Apple II. The second condition narrowed consideration to the several industrial microcomputer/ microcontroller boards designed for use with ASR serial terminals, and for using the terminal's local storage facility (originally, the paper-tape facility of the ASR 33 Teletype) for memory loading and dumping and the keyboard of the terminal for control commands, including the command to begin execution at a specified location in memory. The boards in this category included the JOLT and the SUPERJOLT, the KIM-I, the SYM, the SUPERKIM, and the AIM-65. We selected the KIM-I, at $159 the second cheapest of the above boards, primarily because the second author was already thoroughly familiar with this unit, having used it as the central component of his personal computer system. With 30 digital input/output (I/O) lines and two precision timers, it clearly had the capability for taking over the task of monitoring and recording subject responses while the Apple dealt with precise presentation of experimental stimuli. The Hardware Interface While the serial interface of the KIM-I is designed for 20-rnA current-loop operation, serial information is actually sent and received for processing at standard 5-V transistor-to-transistor logic (TTL) levels. Hence, we decided to attach the interface cable to the KIM with clip-on connectors bypassing the 20-rnA current-loop circuits. The resulting interface is shown in Figure 1. In keeping with our decision to minimize design time, we did not bother to balance the transmission line. The interface shown in Figure 1 works fine to 3 kbaud. KIM-I firmware limits transmission rates to 9.6 kbaud in any case, and the relative improvement obtainable by designing a balanced-line interface would have been limited to that rate. Apart from connectors, the interface shown in Figure 1 consists of three wires and one resistor. On the Apple II side of the interface, a single KIM-l is attached to Input SWO and to Output ANO. Three KIM-Is could be connected by using SWO-SW2 and ANO-AN2. A multiplexer routing SWO and ANO according to ANI-AN3 may be used with existing software to run a network comprising up to seven KIM-Is, with one of the eight possible multiplexer codes reserved for loading and starting all the satellites simultaneously. SOFTWARE Teletype Emulation In developing network control software for the Apple II, we minimized development work by making maximum use of published software. Sender software for LOW-COST MICROCOMPUTER NETWORKING "f1 ""D TA,e t/o 223 r-------tA.-A cdltTItDi. TTY nOD RTltll II'. ... PBS....--...;''-i H) a: o It 4' • l- ! v z z ItITVIt.. OATIt UI o u TTY OTIt IITRH (~I TTY 1C1ID .J C ... ...err: 0: X CI 1147 Go cltS ...----4--+---+---_~ A-I Go ellIS TT PT 2 MEGOHMS vee (+5v.) Figure 1. Circuit diagram of the KIM-I TTY interface circuit and the Apple 11/ KIM-I network interface connection. Teletype emulation was adapted from the TTYDRNER program (see Apple Computer, Inc., Note I, p. 119) by R. Wigginton and S. Wozniak. This program was revised to run at 30 times its original baud rate. The KIM-I TrY input routine was adapted to the hardware available on the Apple II by replacing its timing subroutines by corresponding subroutines from TTYDRNER (Apple Computer, Inc., Note 1), again modified to run at 3 kbaud. NetworkControl A IK area of the Apple's memory was set aside for an input map of the KIM's memory. We then wrote a program for the Apple that uses the KIM's built-in TTY dump routine to transfer an exact map of all of KIM's RAM (except for the stack area in the top half of Page 1) to the map area in the Apple. A similar program transfers the content of a similar IK-byte "output map" area from the Apple to the KIM (taking care not to overwrite RAM locations used by the KIM TrY load routines the program invokes). A third Apple program starts the KIM at a location in KIM-I RAM specified by 4 bytes of RAM in the Apple II. A fourth program for the Apple sends out a synchronization pulse that can be read by the sequence BIT 1740 other. Finally, we insure the transfer of control back to the Apple by having the Apple wait for its input to go high. The KIM is programmed to return to "TrY" control by ending its program with an unconditional JMP IDBC. Since all Apple II programs are also usable as subroutines, it was a simple matter to combine the above programs into two programs used in actual applications of the network. The first of these maps from the Apple to the KIM and then starts the latter at the desired location. The second waits until the KIM returns to Apple control and then maps the KIM to the Apple. Each of these programs takes approximately 15 sec. This is not an unreasonable amount of time, especially since the KIM has an unbroken block of 512 locations usable for data storage. This is enough to store 4 bytes of data from each of 128 trials, a reasonable size for a session in most psychological experiments. If the amount of storage or I/O in the KIM proves inadequate, it may be readily expanded, or additional nodes may be added to the network, and so on. REFERENCE NOTE I. Apple Computer Inc. Apple 11 R(/ennce Mtlnlltll. Apple Part No. 03().()()()4-(J(). Cupertino, Calif: Author. (Available from Computer, Inc., 10260 Bandley Drive, Cupertino, California 9SOl4). BPL#FB when this sequence is executed by the KIM-I. This simple protocol synchronizes the satellite node(s) to within 6 microsec with the central node and with each REFERENCE A. V. Microcomputer display timil1l: Problems and solutions. Belulvior RU«lrch Methods tl Instrumentation, 1979, 11, S72-S76. REED, 224 REED, LEWART, AND SCHNEIDER Appendix A Network Software Memory Map (Apple D) 9200-95FF Map of KIM for next invocation of BAOO or 8C40 8EOO-9lFF Map of KIM from last invocation of 8BOO or 8C40 8AOC 8A82 8BOO 8COO 8000 Accept one character from Kim into A. OUtput character in A to KIM. Map KIM to Apple (16 sec): 0000-017F to 8EOO-8F7F l780-l7FF to 8F80-8FFF 0200-03FF to 9000-91FF· Map Apple to KIM (12 sec); 9200-92EF to OOOO-OOEF 9300-937F to 0100-017F 9380-93EF to l780-l7EF 9400-95FF to 0200-03FF. Start KIM at the indicated IDea t i on . The command format is *HHHH SOOOG, where HHHH is the starting address for the KIM. 8063 Transfer control back to Apple after KIM does 8033 JMP lDBC. Send a synchronization pulse to be read by the KIM loop BIT 1740; BPL loop. 8D2A Synchronize (8D33), then wait until KIM returns 8040 Map Apple to KIM; start KIM at desired location; control (8063). wai t until KIM returns control; then map KIM to Apple. Command format analogous to 8DOO. Takes 30 sec plUS time to execute KIM program. Appendix B Network Software Listing ....SAOO8A028A04BA068AOE'SA09BAOA8AOBBAOC- eaoo- 8ROEBAOFSA10SA12SAIS8A17BAIA8A1DSA20BA228A248A268A28BA2A8A2D8A2ESA308A3::".8A348A358A::'E.- 8A37BA398A388A3C8A3DBA3ESA3F8A408A428A44- A9 DC 85 3S A9 SA 85 39 60 00 00 00 SA 48 9S 48 A2 08 2C 61 CO 10 FB 20 40 8A 20 44 8A AD 61 CO 49 FF 29 80 46 4A 05 4A S5 4A 20 40 8A CA DO ED 20 44 8A 68 A8 68 AA R~, 4A 09 80 60 00 00 00 00 A9 09 DO 02 A9 04 LDA STA LDR STA RTS BRK BRK BRK TXA PHA TYA PHA LDX BIT BPL JSR ,JSR LDA EOR AHD LSR ORA STA JSR DEX B~IE .J8R PLA TRY PLA TRX LDA ORA RTS BRK BRK BRK BRI< LOA 8NE LDA .SOC $38 "SSA $39 .SOB SC061 S8A12 SBA40 SSA44 .e061 .SFF .S80 S4A S4A S4A S8A40 S8A1D SSA44 .4A .SSO .S09 .SA46 .S04 SA46SA47SA49SA4AflA4CSA4D8A4FSA518ASSSA578AS9SASBSASD8A5FSA61SA638A64SA6S8A66SA67SA68SA6A8A6BSA6O8A6FSA70SA72SA748A76BA7B8A7ABA7CSA7E8A818A828AS38A84BA87BAS98ASASABCSA8D8ASFSA92SA948A978A9A8A9BSA9C8R9ESARO8ARtSAA3SAA6SAA88AAB8ARDBABO8AB3SAB58AB78AB9BABBBABD8ABFSAC 08ACt8AC48AC58AC78AC8SAC98ACB8ACESADO8AD3BAD58A068AD88AD98ADB8ADC8ADE8AEOSAE1SRE28RE3- 48 AS' 20 4A 90 FO 68 ES' 01 DO F5 60 S6 3F 29 7F 49 30 e9 OA 90 02 69 SS A2 03 OA OA OA OA OA 2'::' 3E CA 10 FA A6 3F 60 A9 S2 SS 36 A9 SA S5 37 A9 48 85 21 A5 24 8D FB 60 48 48 AD F8 CS 24 68 80 03 4S A9 AO 2C CO FO 03 EE F8 20 C1 68 48 90 E6 49 OD OA 00 OD BD FS A9 8A 20 C1 AS' 58 20 A8 AD F8 FO 08 E5 21 E9 F7 90 04 €>9 1F BS 24 68 60 8e F7 OS AO OB 18 48 80 05 RD ~9 90 03 AO 58 A9 09 48 A9 20 4A 90 FD 6S E9 01 DO FS 68 6A 88 DO E3 8A 8A 8A SA 8A SA 8A Fe BA SA PHA LOA LSR Bee PLA SBe BHE RTS STX A....O EOR CMP BCC AOC LOX ASL. ASL. ASL. ASL. ASL. ROL. OEX BPL. LDX RTS LDA STA LDA STA LOA STA LDA STA RTS PHA PHA LDA CMP PLR BCS PHA LOA BIT BEQ INC ,JSR PLA PHR BCC EOR ASL. B....E STA LDA ,JSR LDA JSR LDA BEQ SBC SBC Bce ADC STA PL.A RTS STV ...20 .SA49 •• 01 .SA46 S3F .. S7F .S30 "SOA SSA61 .. see .S03 S3E S8A67 S3F .. SS2 S36 ..S8A S37 .. S48 S21 S24 S8AFS S8AFS s24 SSA9F "SAO saRCO SSR97 S8AF8 S8AC1 S8A84 "SOD SSABO S8AFS .. S8A S8ACl .. S5B 'FCAS S8AF8 .8ABO S21 . .F7 SSABF .$lF .24 SBAF7 PHP CO CO LOV CL.C PHA BCS LOA BCC LDA LDA PHA LOA LSR Bce PLA sac B....E PLA ROR DEY B....E "OB S8RDO SC059 seAD3 SC058 .. S09 .. S20 S8ADS .S01 S8RDS SSRC8 LOW-COST MICROCOMPUTER NETWORKING 8AE58AESSAE9- AC F7 SA 2S 60 LOY PLP RTS $SAF7 S80088038B05S808SBOA8800S80F8811S8138815S81SS819S81BS810SB20S823S826S829S8288820882ES830S831S8338835S836S83SSB3AS83CS83ES841S843S845S84SS84AS84CS84ES851S853S855885SS859S85C885FS862S863S865S867SB69S868S86DS86F8872S8738875887688788879S87888;'08B7F88B1S8S2S8S5S887S8SAS88D8SSFS8928894S896S898889A88908COOSC01SC03SC068C089C09scooSCOF- 4C 87 A9 51 20 82 AD 00 20 OC 29 7F C9 38 DO F7 A2 06 20 OC CA DO FA A2 lS 20 DC 20 55 20 DC 20 55 A5 3E 91 42 C8 30 05 CA DO EA FO 05 60 A9 00 S5 42 A9 8E S5 43 20 03 S4 42 AD 00 20 30 AO 00 S4 42 E6 43 20 30 S4 42 AO 00 20 30 60 20 36 20 4S 20 48 60 A9 AD S5 42 A9 88 S5 43 81 42 30 OE 20 82 C8 DO F6 C8 84 46 60 AD 00 FO EE. 29 7F FO F4 OA 20 A8 FO EB 20 79 20 59 A4 46 20 63 A9 SO 8'5 42 A9 SF S5 43 20 03 60 OS A9 4C 20 82 A9 38 20 S2 A9 00 85 FS S~ F9 .JMP LOA ,JSR LOY ,JSR AHO CMP BHE LOX ,JSR OEX 8HE LOX 3SR ,JSR ,JSR ,JSR LOA STA IHY 8MI OEX 8HE BEQ RTS LOA STA LOA STA 3SR STY LOY 3SR LOY STY IHC ,JSR STY LOY 3SR RTS ,JSR ,JSR 3SR RTS LOA STA LOA STA LOA 8MI 3SR IHY BHE IHY STY RTS LOY 8EQ AND 8EQ ASL ,JSR 8EQ ,JSR 3SR LOY JSR LOA $SBS7 .$51 $SAS2 "$00 $SAOC .$7F . .38 SSBOA .$06 $SAOC S8 SA SA 8A SA SA SA SA S8 S8 S8 S8 88 S8 S8 SA FC S8 SB 88 STA S8 SA 8A LOA STA ,JSR RTS CLO LOA 3SR LOA ,JSR LDR STA STA $SB15 .$1S SSAOC $eA:55 SSAOC $SA:55 S3E <$42), Y .S835 .SB10 $S80A .$00 $42 "SSE .43 $SB03 $42 "SOO $S830 "SOO .42 S43 .SB30 $42 .SOO $SB30 $SB36 .SB4S .SB4S "$AO .42 .SS8 .43 <S42),Y .SB7D $SAS2 $8868 $46 .$00 .SB63 .$7F S8B75 SFCAS $S872 $S879 $8859 .46 $S863 41$80 $42 4I$SF .43 $8803 .. S4C .SAS2 .$38 .8A82 "$00 SFe SF9 SC11SC13SC1:5SC1SSC1ASC10SC1FSC22SC24SC27SC29SC28eC20SC30SC32SC3:5SC37SC3ASC30SC3ESC3FSC40SC428C44SC46SC47SC498C48SC4CSC4ESC50SC52SC:53SC5:5SC57SC59SC58SC5CSC5FSC61SC64SC66SC69SC68SC60SC70SC728C74SC76SC7SSC7A8C7CSC7DSC7FSCS28C84SCS7SC898caB8CSDSCBF8C908C928C958C978C998C9ASC98BC9CSC9DSCAOSCA2SCA4SCA68CASSCAA8CADSCAFSCBO8CB38C84SC868CBSSCBA8CBCSCBD6CBE- 8CBF- AD A2 20 A2 20 A2 20 S4 20 A4 DO A9 20 A:5 20 A5 20 4C 00 00 00 A9 S:5 S5 3S A:5 E5 AA A5 E5 DO 8A FO C9 90 A9 AA 20 A5 20 A5 20 AD 81 20 EE. DO E6 E6 DO E6 CA DO 20 A9 20 E6 DO EE. DO 60 A5 20 A5 85 4A 4A 4A 4A 20 29 C9 90 69 69 20 A5 60 20 18 65 85 90 E6 60 00 00 00 ES E7 CO SC EA CO SC FA CO SC FO 40 SC FO ES 00 97 SC F9 80 SC F8 eo SC 90 SC 00 F6 F7 E7 FA ES F8 07 3A CO 02 CO BO se E8 80 8C EA 80 8C 00 FA 80 BC EA 02 E8 FA 02 FB EA 90 se 38 82 8A FS 85 F9 81 F6 97 8C F7 FC A2 SC OF OA 02 DE. 30 82 SA FC '37 Be F7 F7 02 F6 LOY LOX 3SR LOX 3SR LOX ,JSR STY ,JSR LOY 8HE LOA 3SR LOA 3SR LOA 3SR 31'1P BRI< 8RI< BRK LOA STA STA SEC LOA S8C TAX LOA S8C 8HE TXA BEQ CMP 8CC LOA TAX .JSR LOA ,JSR LOA ,JSR LOY LOA ,JSR INC SNE INC INC SHE IHC OEX 8HE .JSR LOA ,JSR IHC BHE INC SNE RTS LOA ,JSR LOA STA LSR LSR LSR LSR 3SR AND CMP 8CC AOC AOC .JSR LOA RTS .JSR CLC ROC STA 8CC INC RTS SRK BRK 8RK "ES "$E7 $SCCO UEA $SCCO "$FA $SCCO $FO $SC40 $FO $SC13 "SOO $SC97 SF9 $Sceo SFS sacac $eC90 .SOO $F6 $F7 $E7 'FA 'ES $F8 .SC:59 $SCSF "SCO .SC:58 .SCO 'SC80 .E8 $SC80 SEA $SC80 .$00 <SFA), 'y' SSC80 $EA $SC76 $E8 $FA SSC7C .F8 .SC69 S8C90 .$3B SSAS2 $FS .BC40 .F9 $SC40 $F6 .8C97 $F7 'Fe $SCA2 .SOF "SOA 'SCAB .. S06 .$30 $SA82 'FC SSC97 .F7 .F7 SSCBC .F6 225 226 REED, LEWART, AND SCHNEIDER 8CCO8CC38CC48CC78CC98CCA8CCB8CCC8000800380068009800C800F801280158018801B801ES0208023802:5S02SS029S02A8020803080318032803380368039803C8030803ES03F8040S0438045S0488041'18040805080538055- 20 E8 B9 95 C8 60 00 00 AD 20 AO 20 AD 20 AO 20 AO 20 A9 20 A9 20 60 00 20 20 60 00 00 2C 2C 2C 60 00 00 00 20 A9 20 A9 20 20 20 A9 20 C4 8C E8 88 00 00 02 82 SA 01 02 828A 02 02 82 8A 03 02 S2 8A 04 02 82 8A AS A8 FC 47 S2 81'1 33 80 63 SO 59 CO 59 CO 58 CO 00 FF AS FF A8 00 63 FF A8 8C FC FC 80 80 FC J'SR IHX LOA STA IHY RTS BRK BRK LOA J'SR LOA J'SR LOA 3SR LOA J'SR LOA J'SR LOA J'SR LOA J'SR RTS BRK J'SR 3SR RTS BRK BRK BIT BIT BIT RTS BRK BRK BRK 3SR LOA .JSR LOA .JSR J'SR .JSR LOA .JSR $8CC4 $8BE8,Y $OO,X $0200 $SA82 $0201 $8A82 .0202 $8A82 $0203 $8AS2 $0204 $8A82 .$A8 $FCA8 ••47 $8AS2 8058805A805080608061806:2806380668068806A806C80608BAO8BA88BBO88888BCO8BC8~ ecoo$S033 $S063 SCOS8CEOSCE8SCFO8CF8- ll$FF $FCA8 $8BOO A9 FF 20 A8 FC 20 00 8B 60 00 00 20 OC 8A 29 7F C9 20 00 F7 60 00 31 37 46 37 2E 04 30 33 04 SO FF FF 20 04 46 46 2E 04 31 37 SO 00 00 00 LOA J'SR J'SR RTS BRK BRK J'SR AHO CMP BHE RTS BRK 20 04 2E 04 31 37 2E 04 38 30 00 00 46 30 46 31 20 00 46 20 37 37 03 00 FO 00 80 00 00 00 00 FO 00 00 00 00 80 SO 00 00 00 00 93 17 94 00 00 00 92 01 93 00 00 00 00 00 00 00 00 00 00 93 CO 00 00 00 .92 ·93 02 00 00 00 $8AOC .$7F .$20 $8063 SC059 .CO~9 SCOS8 Appendix C Network Initialization Procedure for Satellites $8COO .$FF $FCA8 .$FF $FCA8 $8000 $8063 ••FF $FCA8 1. Set KIM-l KBD-TTY switch to KBD. 2. Press the following sequence of keys on the KIM keyboard: (RS) (AD) 17F2 (DA) 18 (+) 00 (AD) This sequence sets the baud rate to 3,000 baud. 3. Set the KBD-TTY switch to TTY. 4. Run appropriate network software from the Apple II.
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