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Where does the Z80 processor start executing from?


How did the Z80 instruction set differ from the 8080?Why does the Z80 have a half-carry bit?How fast is memcpy on the Z80?z80 crashes after executing some instructionsWhy does the Z80 include the RLD and RRD instructions?Why is the Z80's supply pin in the middle of the data pins?Why did TI-8x calculator series use the Z80 processor?Role of the Z80 co-processor in GBA gamesHow do I Interface a PS/2 Keyboard without Modern Techniques?What does ld a,(hl) do in this piece of Z80 ASM code, and why is HL incremented?













4















Strangely I can't find this information anywhere online -- I've thoroughly looked at the datasheet, and I've searched things like "Z80 program counter initial value" -- but I can't find anything!



My question is simply: when the Z80 just turns on, what value does the program counter take? (i.e., what instruction does it start executing from?)



Logically, I'd assume it initialises to 0, but I want to be sure of this.










share|improve this question







New contributor




Jacob Garby is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
























    4















    Strangely I can't find this information anywhere online -- I've thoroughly looked at the datasheet, and I've searched things like "Z80 program counter initial value" -- but I can't find anything!



    My question is simply: when the Z80 just turns on, what value does the program counter take? (i.e., what instruction does it start executing from?)



    Logically, I'd assume it initialises to 0, but I want to be sure of this.










    share|improve this question







    New contributor




    Jacob Garby is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
    Check out our Code of Conduct.






















      4












      4








      4








      Strangely I can't find this information anywhere online -- I've thoroughly looked at the datasheet, and I've searched things like "Z80 program counter initial value" -- but I can't find anything!



      My question is simply: when the Z80 just turns on, what value does the program counter take? (i.e., what instruction does it start executing from?)



      Logically, I'd assume it initialises to 0, but I want to be sure of this.










      share|improve this question







      New contributor




      Jacob Garby is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.












      Strangely I can't find this information anywhere online -- I've thoroughly looked at the datasheet, and I've searched things like "Z80 program counter initial value" -- but I can't find anything!



      My question is simply: when the Z80 just turns on, what value does the program counter take? (i.e., what instruction does it start executing from?)



      Logically, I'd assume it initialises to 0, but I want to be sure of this.







      z80






      share|improve this question







      New contributor




      Jacob Garby is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.











      share|improve this question







      New contributor




      Jacob Garby is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.









      share|improve this question




      share|improve this question






      New contributor




      Jacob Garby is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.









      asked 3 hours ago









      Jacob GarbyJacob Garby

      1233




      1233




      New contributor




      Jacob Garby is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.





      New contributor





      Jacob Garby is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.






      Jacob Garby is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.




















          1 Answer
          1






          active

          oldest

          votes


















          6














          Yes, it's zero - like the 8080 it descends from.



          Excerpt from Zilog's March 1978 Product Specification (datasheet), page 2, Pin Description, here the /RESET signal (emphasis mine):




          Input, active low. RESET initializes the CPU as follows:
          reset interrupt enable flip-flop, clear PC and registers
          I and R and set interrupt to 8080A mode.




          Similar the description in the 1977 Z80 Technical Manual (03-0029-01) on page 9.






          share|improve this answer

























          • Thanks! I actually didn't know that the 8080 started at zero either, but it makes complete sense.

            – Jacob Garby
            3 hours ago











          • (I'll accept the answer as soon as I can)

            – Jacob Garby
            3 hours ago











          • Does anything not start at zero?

            – dashnick
            1 hour ago






          • 3





            @dashnick Many don't just start, but take a vector form a predefined location like 6500 and 6800 start at the vector residing at FFFE/FF, 68k takes the initial PC from Vector 1 (address 4..7). Other do start form some address where the IOC locates a loader record, and so on. Starting from Zero is only one of many ways.

            – Raffzahn
            44 mins ago






          • 2





            Intels 8086 employs an interesting combination by starting a offset zero, like 8080/Z80, but in segment FFFF, thus at absolute address FFFF0.

            – Raffzahn
            22 mins ago










          Your Answer








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          1 Answer
          1






          active

          oldest

          votes








          1 Answer
          1






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes









          6














          Yes, it's zero - like the 8080 it descends from.



          Excerpt from Zilog's March 1978 Product Specification (datasheet), page 2, Pin Description, here the /RESET signal (emphasis mine):




          Input, active low. RESET initializes the CPU as follows:
          reset interrupt enable flip-flop, clear PC and registers
          I and R and set interrupt to 8080A mode.




          Similar the description in the 1977 Z80 Technical Manual (03-0029-01) on page 9.






          share|improve this answer

























          • Thanks! I actually didn't know that the 8080 started at zero either, but it makes complete sense.

            – Jacob Garby
            3 hours ago











          • (I'll accept the answer as soon as I can)

            – Jacob Garby
            3 hours ago











          • Does anything not start at zero?

            – dashnick
            1 hour ago






          • 3





            @dashnick Many don't just start, but take a vector form a predefined location like 6500 and 6800 start at the vector residing at FFFE/FF, 68k takes the initial PC from Vector 1 (address 4..7). Other do start form some address where the IOC locates a loader record, and so on. Starting from Zero is only one of many ways.

            – Raffzahn
            44 mins ago






          • 2





            Intels 8086 employs an interesting combination by starting a offset zero, like 8080/Z80, but in segment FFFF, thus at absolute address FFFF0.

            – Raffzahn
            22 mins ago















          6














          Yes, it's zero - like the 8080 it descends from.



          Excerpt from Zilog's March 1978 Product Specification (datasheet), page 2, Pin Description, here the /RESET signal (emphasis mine):




          Input, active low. RESET initializes the CPU as follows:
          reset interrupt enable flip-flop, clear PC and registers
          I and R and set interrupt to 8080A mode.




          Similar the description in the 1977 Z80 Technical Manual (03-0029-01) on page 9.






          share|improve this answer

























          • Thanks! I actually didn't know that the 8080 started at zero either, but it makes complete sense.

            – Jacob Garby
            3 hours ago











          • (I'll accept the answer as soon as I can)

            – Jacob Garby
            3 hours ago











          • Does anything not start at zero?

            – dashnick
            1 hour ago






          • 3





            @dashnick Many don't just start, but take a vector form a predefined location like 6500 and 6800 start at the vector residing at FFFE/FF, 68k takes the initial PC from Vector 1 (address 4..7). Other do start form some address where the IOC locates a loader record, and so on. Starting from Zero is only one of many ways.

            – Raffzahn
            44 mins ago






          • 2





            Intels 8086 employs an interesting combination by starting a offset zero, like 8080/Z80, but in segment FFFF, thus at absolute address FFFF0.

            – Raffzahn
            22 mins ago













          6












          6








          6







          Yes, it's zero - like the 8080 it descends from.



          Excerpt from Zilog's March 1978 Product Specification (datasheet), page 2, Pin Description, here the /RESET signal (emphasis mine):




          Input, active low. RESET initializes the CPU as follows:
          reset interrupt enable flip-flop, clear PC and registers
          I and R and set interrupt to 8080A mode.




          Similar the description in the 1977 Z80 Technical Manual (03-0029-01) on page 9.






          share|improve this answer















          Yes, it's zero - like the 8080 it descends from.



          Excerpt from Zilog's March 1978 Product Specification (datasheet), page 2, Pin Description, here the /RESET signal (emphasis mine):




          Input, active low. RESET initializes the CPU as follows:
          reset interrupt enable flip-flop, clear PC and registers
          I and R and set interrupt to 8080A mode.




          Similar the description in the 1977 Z80 Technical Manual (03-0029-01) on page 9.







          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited 2 hours ago









          George Phillips

          3,5211522




          3,5211522










          answered 3 hours ago









          RaffzahnRaffzahn

          54k6132218




          54k6132218












          • Thanks! I actually didn't know that the 8080 started at zero either, but it makes complete sense.

            – Jacob Garby
            3 hours ago











          • (I'll accept the answer as soon as I can)

            – Jacob Garby
            3 hours ago











          • Does anything not start at zero?

            – dashnick
            1 hour ago






          • 3





            @dashnick Many don't just start, but take a vector form a predefined location like 6500 and 6800 start at the vector residing at FFFE/FF, 68k takes the initial PC from Vector 1 (address 4..7). Other do start form some address where the IOC locates a loader record, and so on. Starting from Zero is only one of many ways.

            – Raffzahn
            44 mins ago






          • 2





            Intels 8086 employs an interesting combination by starting a offset zero, like 8080/Z80, but in segment FFFF, thus at absolute address FFFF0.

            – Raffzahn
            22 mins ago

















          • Thanks! I actually didn't know that the 8080 started at zero either, but it makes complete sense.

            – Jacob Garby
            3 hours ago











          • (I'll accept the answer as soon as I can)

            – Jacob Garby
            3 hours ago











          • Does anything not start at zero?

            – dashnick
            1 hour ago






          • 3





            @dashnick Many don't just start, but take a vector form a predefined location like 6500 and 6800 start at the vector residing at FFFE/FF, 68k takes the initial PC from Vector 1 (address 4..7). Other do start form some address where the IOC locates a loader record, and so on. Starting from Zero is only one of many ways.

            – Raffzahn
            44 mins ago






          • 2





            Intels 8086 employs an interesting combination by starting a offset zero, like 8080/Z80, but in segment FFFF, thus at absolute address FFFF0.

            – Raffzahn
            22 mins ago
















          Thanks! I actually didn't know that the 8080 started at zero either, but it makes complete sense.

          – Jacob Garby
          3 hours ago





          Thanks! I actually didn't know that the 8080 started at zero either, but it makes complete sense.

          – Jacob Garby
          3 hours ago













          (I'll accept the answer as soon as I can)

          – Jacob Garby
          3 hours ago





          (I'll accept the answer as soon as I can)

          – Jacob Garby
          3 hours ago













          Does anything not start at zero?

          – dashnick
          1 hour ago





          Does anything not start at zero?

          – dashnick
          1 hour ago




          3




          3





          @dashnick Many don't just start, but take a vector form a predefined location like 6500 and 6800 start at the vector residing at FFFE/FF, 68k takes the initial PC from Vector 1 (address 4..7). Other do start form some address where the IOC locates a loader record, and so on. Starting from Zero is only one of many ways.

          – Raffzahn
          44 mins ago





          @dashnick Many don't just start, but take a vector form a predefined location like 6500 and 6800 start at the vector residing at FFFE/FF, 68k takes the initial PC from Vector 1 (address 4..7). Other do start form some address where the IOC locates a loader record, and so on. Starting from Zero is only one of many ways.

          – Raffzahn
          44 mins ago




          2




          2





          Intels 8086 employs an interesting combination by starting a offset zero, like 8080/Z80, but in segment FFFF, thus at absolute address FFFF0.

          – Raffzahn
          22 mins ago





          Intels 8086 employs an interesting combination by starting a offset zero, like 8080/Z80, but in segment FFFF, thus at absolute address FFFF0.

          – Raffzahn
          22 mins ago










          Jacob Garby is a new contributor. Be nice, and check out our Code of Conduct.









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