Timeline for How can a Z80 assembly program find out its own memory address?
Current License: CC BY-SA 4.0
26 events
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| Feb 14, 2020 at 2:54 | comment | added | Jean-François Fabre | okay, maybe someone wants to edit the answer so the z80 code is correct? | |
| Feb 12, 2020 at 20:23 | comment | added | CJ Dennis |
Unfortunately ld af,(sp) makes no sense for a Z80. 1. AF is the (8-bit) Accumulator A and (8-bit) Flag F registers, never treated as a 16-bit value except when PUSHing, POPping, or EXchanging. You would want to use one of BC, DE, or HL. 2. You can't get (SP) except by POPping which also adds 2 to SP. So you'd want to POP BC, POP DE, or POP HL.
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| Feb 12, 2020 at 19:36 | comment | added | Misha Lavrov |
If something like call next followed by next: pop hl works, then so does next: ld hl, next. In either case, this is only valid if the address of the code is known at compile time.
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| Feb 11, 2020 at 21:45 | comment | added | S.S. Anne | I wouldn't load it into AF. AF is the flags register and that could be dangerous. | |
| Feb 11, 2020 at 15:58 | comment | added | Criticizing Israel not allowed | @ilkkachu I can comfirm the PIC12F508 (page 27) has an inaccessible stack. But we're talking about a machine with 25 bytes of RAM here. The hidden stack adds another 3 whole bytes! (2 x 12 bits) | |
| Feb 11, 2020 at 13:21 | comment | added | Raffzahn | @ilkkachu Hihi. Yes, that would add another level of fun :) | |
| Feb 11, 2020 at 13:20 | comment | added | Raffzahn | @another-dave Sure, that needs to be defined before anything else. But when done, it's simply a subtraction of the offset from the instructions address. Ofc, this can only be valid when done in the same module (phase) as the defined start is :) So yes, there are many additional hurdles that could apply. For a definite answer more information is needed than given by the OP. | |
| Feb 11, 2020 at 13:03 | history | edited | Jean-François Fabre | CC BY-SA 4.0 |
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| Feb 11, 2020 at 10:55 | comment | added | ilkkachu | ...for all processors with a software-accessible call stack ;) There might be ones with a hidden call stack, accessible only by the call and return instructions. I think some tiny RAM-less AVR might have had something like this. | |
| Feb 11, 2020 at 8:48 | history | edited | Alex Hajnal | CC BY-SA 4.0 |
FIxed typos
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| Feb 11, 2020 at 7:37 | history | edited | Jean-François Fabre | CC BY-SA 4.0 |
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| Feb 11, 2020 at 7:35 | comment | added | Jean-François Fabre | yeah simple pc relative lea does the job. | |
| Feb 11, 2020 at 7:26 | comment | added | lvd |
for 68k it is as simple as lea (pc),a0
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| Feb 11, 2020 at 2:54 | comment | added | dave | To be picky: this answer and others tell how to get the address of a particular instruction, The "address of the program" is a little trickier, starting with defining what that really means. | |
| Feb 11, 2020 at 2:49 | comment | added | dave | If there's no call stack then it's probably even easier, The return address will get stored somewhere -- register, first word of subroutine, … :-) | |
| Feb 11, 2020 at 0:27 | comment | added | RETRAC | Only works for processors with a subroutine call stack :) | |
| Feb 10, 2020 at 22:27 | comment | added | Jean-François Fabre | I only know z80 through disassembling arcade games. Never coded anything with that processor myself... | |
| Feb 10, 2020 at 22:26 | history | edited | Jean-François Fabre | CC BY-SA 4.0 |
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| Feb 10, 2020 at 22:26 | comment | added | user722 | Don't really know Z80 well myself, I had to Google about the JR instruction. | |
| Feb 10, 2020 at 22:25 | history | edited | Jean-François Fabre | CC BY-SA 4.0 |
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| Feb 10, 2020 at 22:22 | comment | added | Jean-François Fabre | I see, no need to return from the subroutine, I get it.. please feel free to edit the z80 code of the answer above. I can use a good z80 lesson | |
| Feb 10, 2020 at 22:21 | comment | added | user722 |
AF is the flags register and JR doesn't push a return value. You could simplify this with something like call next next: pop ix. Though CALL isn't relative.
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| Feb 10, 2020 at 22:20 | history | edited | Jean-François Fabre | CC BY-SA 4.0 |
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| Feb 10, 2020 at 22:09 | history | edited | Jean-François Fabre | CC BY-SA 4.0 |
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| Feb 10, 2020 at 22:08 | vote | accept | twisted | ||
| Feb 11, 2020 at 18:41 | |||||
| Feb 10, 2020 at 22:02 | history | answered | Jean-François Fabre | CC BY-SA 4.0 |