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Where does the Z80 processor start executing from?
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Where does the Z80 processor start executing from?
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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
asked 3 hours ago
Jacob GarbyJacob Garby
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.
add a comment |
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
asked 3 hours ago
Jacob GarbyJacob Garby
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.
add a comment |
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
asked 3 hours ago
Jacob GarbyJacob Garby
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.
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
z80
asked 3 hours ago
Jacob GarbyJacob Garby
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.
asked 3 hours ago
Jacob GarbyJacob Garby
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.
asked 3 hours ago
Jacob GarbyJacob Garby
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.
asked 3 hours ago
Jacob GarbyJacob Garby
1233
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.
add a comment |
add a comment |
1 Answer
1
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oldest
votes
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.
edited 3 hours ago
George Phillips
3,5211522
answered 3 hours ago
RaffzahnRaffzahn
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
4
@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
47 mins ago
3
Intels 8086 employs an interesting combination by starting a offset zero, like 8080/Z80, but in segment FFFF, thus at absolute address FFFF0.
– Raffzahn
26 mins ago
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
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active
oldest
votes
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.
edited 3 hours ago
George Phillips
3,5211522
answered 3 hours ago
RaffzahnRaffzahn
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
4
@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
47 mins ago
3
Intels 8086 employs an interesting combination by starting a offset zero, like 8080/Z80, but in segment FFFF, thus at absolute address FFFF0.
– Raffzahn
26 mins ago
add a comment |
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.
edited 3 hours ago
George Phillips
3,5211522
answered 3 hours ago
RaffzahnRaffzahn
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
4
@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
47 mins ago
3
Intels 8086 employs an interesting combination by starting a offset zero, like 8080/Z80, but in segment FFFF, thus at absolute address FFFF0.
– Raffzahn
26 mins ago
add a comment |
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.
edited 3 hours ago
George Phillips
3,5211522
answered 3 hours ago
RaffzahnRaffzahn
54k6132218
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.
edited 3 hours ago
George Phillips
3,5211522
answered 3 hours ago
RaffzahnRaffzahn
54k6132218
edited 3 hours ago
George Phillips
3,5211522
edited 3 hours ago
George Phillips
3,5211522
edited 3 hours ago
George Phillips
3,5211522
3,5211522
answered 3 hours ago
RaffzahnRaffzahn
54k6132218
answered 3 hours ago
RaffzahnRaffzahn
54k6132218
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
4
@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
47 mins ago
3
Intels 8086 employs an interesting combination by starting a offset zero, like 8080/Z80, but in segment FFFF, thus at absolute address FFFF0.
– Raffzahn
26 mins ago
add a comment |
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
4
@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
47 mins ago
3
Intels 8086 employs an interesting combination by starting a offset zero, like 8080/Z80, but in segment FFFF, thus at absolute address FFFF0.
– Raffzahn
26 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
4
4
@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
47 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
47 mins ago
3
3
Intels 8086 employs an interesting combination by starting a offset zero, like 8080/Z80, but in segment FFFF, thus at absolute address FFFF0.
– Raffzahn
26 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
26 mins ago
add a comment |
Jacob Garby is a new contributor. Be nice, and check out our Code of Conduct.
Jacob Garby is a new contributor. Be nice, and check out our Code of Conduct.
Jacob Garby is a new contributor. Be nice, and check out our Code of Conduct.
Jacob Garby is a new contributor. Be nice, and check out our Code of Conduct.
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