RCA CDP18S711 manual V. Logic Description, How Memory Is Addressed, How the Input/Output Works

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V. Logic Description

A complete set of logic diagrams is provided in Appendix E. Power requirements for a system with 2048 bytes of RAM is 5 V DC at 350 mA. If you wish to expand the system you can use your own higher current power supply.

This system is designed around the CDP1802 microprocessor Wfl. Refer to the CDP1802 data sheet and User Manual for the CDPI802 COSMAC Microprocessor MPM-201Afor a complete description of its operation. The CDP1802 requires a square-wave clock input at pin 1 for operation. This system uses a 1.7609-MHz clock. One half of U3 is connected as a

free-running crystal-controlled oscillator. A 3.52180-MHz crystal is used in this circuit. The output of this 3.52180-MHz oscillator is then divided by 2 using U4 to provide the 1.7609MHz input clock for the CDP1802. Because each CDP1802 machine cycle equals 8 clock cycles, each machine cycle is about 4.54 us in duration. TPA and TPB are timing pulses generated once each machine cycle by the CDP 1802 microprocessor.

How Memory Is Addressed

A debounced RUN level goes high when the RUN switch is flipped up. This signal causes the CDP1802 to begin fetching instructions from memory. When the RUN switch is down, the CDP1802 is held in a reset state and U6A (in Fig. E-2) is reset. U6B is held set by U6A. The CDP1802 starts fetching instructions from the ROM (U10) at location 8000 since UOB is being held set. The ROM contains the

operating system program which uses a 64 instruction to generate an N2 pulse. This-N2 pulse sets U6A so it no longer holds U6B in its set state. From this point on, the selection,of RAM or ROM locations is controlled by the most significant address bit latched into U6B each cycle by TPA.

U8 latches an additional 4 address bits to provide the 1-9-bit address required in a 4096-byte RAM system. U9A decodes 2 of these address bits into 4 lines which are used to select up to four 1024-byte RAM sections. Each 1024-byte section of RAM consists of two 4 x 1024-bit RAM IC's (U16-U23 in Fig. E-4). Only the first two sections of RAM (U16-U19) are used in a 2048-byte system. U9B in Fig. E-2 is wired as a simple gate that inhibits selecting any section of RAM when either the ROM is selected or a positive RAM inhibit signal is generated on pin 19 of the expansion interface by external circuits.

Memory read (MRD) and write (MWR) signals are supplied to the RAM at appropriate times by the CDP1802. Data is transferred between memory, CDP1802, input, or output via an 8-bit data bus. Pull-up resistors are provided on this bus for compatibility with TTL signal swings provided by some RAMs.

How the Input/Output Works

Ull and U12 in Fig. E-3 are used to decode the input/output instruction codes used in the system.

U13 provides the hex keyboard interface. This interface permits a program to determine which key is

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Contents Page RCA COSMAC VIP CDP18S711 Instruction Manual VIP-311ACKNOWLEDGMENT Contents Contents Continued 1. Getting Started What This Manual CoversThe Power Supply 1. Getting Started What You SeeTurning It On Memory Write Using the Operating System11.COSMAC VIP Operation Tape Read Memory ReadTape Write Testing Your Cassette System 11.COSMAC VIP OperationBranch Instructions How to Change and Use the VariablesIII.CHIP-8Language Programming Using the Display Instructions III. CHIP-8 Language Programming 0200 A20A I=020A 0202 6100 V1=00 0204 6200 V2=000206 D125 SHOW 5MI@VlV2 0208 1208 GO 020A F090 020C F090 020E F000Applying CHIP-8 Some Program Ideas 111. CHIP-8Language Programming25.PROGRAMMED SPOT - Introduce children to programming concepts by letting them preprogram the movements of a spot or object on the screen IV. Machine Language Programming VIP Machine CodingMachine Language Programming Summed Up How the Input/Output Works V. Logic DescriptionHow Memory Is Addressed pressed. A 62 machine instruction causes the least significant 4 bits of memory byte to be latched into U13. These 4 bits are decoded to bring one of the 16 U13 output lines low. If the key that corresponds to this output line is pressed, the CDPI802 EF3 input will go low. The 4-bitcodes latched into U13 correspond to the equivalent key positions. After the program send8 a 4-bitcode to U13, it subsequently examines the EF3 line to see if the key corresponding to this code is pressed or not. In this manner, a program can determine when any specific key is pressed or can sequentially scan all keys while waiting for any one to be pressed. Key debounce delays must be provided in the program when required. A program can also cause a speaker tone to occur when a key is pressed. Only one key at a time should be pressed with this method of interfacing the keyboard Using the Byte Input/Output V1. Expansion Considerations and ConnectionsI RCA COSMAC VIP Instruction Manual Using the Expansion InterfaceSome Expansion Ideas Table III - External Option Terminal Connections Pin SignalV1. Expansion Considerations and Connections 2.Composing poetry or pictures with printer output VIL Troubleshooting Hints Other ProblemsSignal Tracing No SoundLast Resorts Beeper Program Appendix A - Test and Operating DataByte Pattern for Displaying COSMAC Test Program Cassette Attachment Diagram Cassette Phase TestSignals Cassette Data Test Cassette Recording Guidelines Memory Test ProgramAppendix B - Operating System Operating System ListingR3 = Machine Language Subroutine Program Counter Operating System Register TableOperating System Summary Appendix C - CHIP-8Interpreter CHIP-8Interpreter ListingInterpreter CHIP-8Memory MapCDP1802 Register Use for CHIP-8 Appendix C - CHIP-8Interpreter CHIP-8User Notes RCA COSMAC VIP Instruction ManualPage 1. VIP Kaleidoscope 2. VIP Video Display Drawing Game Appendix E - Logic Diagrams Fig. E-5Power Supply Circuit and ByteFig. E-1Microprocessor and Display Interface CircuitsPage Fig. E-2- ROM Circuits and Expansion Interface Appendix E - Logic DiagramsPage Fig. E-4- RAM Circuits Appendix E - Logic DiagramsRCA COSMAC VIP Instruction Manuel RCA COSMAC VIP Instruction Manual Board Layout, Parts List, and Expansion Notes Appendix F2.Parts List for RCA COSMAC VIP CDP18S711 1.Printed Circuit Board LayoutRCA COSMAC VIP Instruction Manual Page 2. Parts List for RCA COSMAC VIP CDP18S711 Page RCA COSMAC VIP Instruction Manual Resistors - Supplied 1 /4 W except as notedPage 3. COSMAC VIP Expansion Notes