Eprom 27256 connection?

Discussion in 'General Electronics Chat' started by vead, Sep 20, 2016.

  1. vead

    Thread Starter Active Member

    Nov 24, 2011
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    Hello
    I am trying to connect 27256 eprom with 74ls163 counter. As my understanding 27256 has A0-A14 address and D0-D7 data bus. Actually I want to see how PC work with ROM memory. I am trying to explain if somewhere wrong. Please correct me.
    ROM is permanent memory, once it programmed. It doesn't change its data.
    Here is small example where data and instructions stored in program memory.
    Code (Text):
    1. Address           data
    2. Address 1        01110000
    3. Address 2        01101110
    4. Address 3        10010001
    Now program counter read first 0111000 and store into instruction register. Than read second second and stored into instruction register same for third, read 10010001 and stored into instructions register. No instructions
    Please look at diagram. If all is correct than I will try to add instructions register.
    _20160920_202133.JPG
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,144
    1,790
    You absolutely cannot have RCO connected to your Enable signal. That would be two outputs driving each other. We had some colorful phrases for two TTL outputs fighting each other.
     
  3. dl324

    Distinguished Member

    Mar 30, 2015
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    The circuit doesn't make much sense to me. Why would you load data from the EPROM into a counter? Using latches would make more sense.

    How are you incrementing the addresses of the EPROM? How are the EPROM control pins being driven? Any chance of tri-stated EPROM outputs being loaded into the counters (which should be latches)?
     
    vead likes this.
  4. vead

    Thread Starter Active Member

    Nov 24, 2011
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    That is some questions whose answer I am searching. I have both ROM and program counter in circuit. Can we start with this circuit just for learning
     
  5. dl324

    Distinguished Member

    Mar 30, 2015
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    The program counter steps you through a program. Does the EPROM contain a program you want to execute?
     
  6. vead

    Thread Starter Active Member

    Nov 24, 2011
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    Yes eprom store data, instruction. I have explained in my first post with example.
    Can you help me to understand how does program counter increment or load address . If possible can you explain with example
     
  7. dl324

    Distinguished Member

    Mar 30, 2015
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    Your first post wasn't very clear.
    Technically, the program counter is just a register that holds the address of the instruction currently being executed. In some computers, it's called CIR (Current Instruction Register). Computers that use CIR will most likely also have an NIR (Next Instruction Register).
     
  8. vead

    Thread Starter Active Member

    Nov 24, 2011
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    Yes I know the definitions of ROM, counter, register. But I need help to understand basic. How they work together. Can we start with very small example
    Program memory
    Address 8 bit wide
    Data 4 bit wide
    Read enable pin
    Program that being to execute
    MOV R1#0010
    MOV R2#0110
    ADD R1,R2

    Program counter
    Data 4 bit wide
    Load pin
    Enable pin
    MOV R1-XXXX, PC read data at address 1
    0010- PC read data at address 1
    MOV R2- PC read data at address 2
    0110- PC read data at address 2
    ADD R1,R2- PC read data at address 3
    Does this make any sense?

    Small memory with small program counter
     
    Last edited: Sep 20, 2016
  9. dl324

    Distinguished Member

    Mar 30, 2015
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    This article seems to have decent information - https://en.wikipedia.org/wiki/Central_processing_unit
     
  10. vead

    Thread Starter Active Member

    Nov 24, 2011
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