6502.org

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With only absolute addressing, you would not be able to pass arguments on the stack anyway.

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If you permit self modifying code, you could build your own data stack in data memory, and then you wouldn't need TSX/TXS at all.

The thing to bear in mind about this topic is that it always is going to be a tradeoff, landing somewhere in between a very-nearly-6502 and a single instruction tarpit.

(Each of us will be inclined to place that tradeoff at a different place. It's all very interesting, but not a good basis to argue over.)

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No, that was my point. You can start the stack at any random point, and it will just wrap around the page boundary, giving you 256 usable bytes.

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But you can set the stack pointer to 0x1ff (well, 0xff) at reset, through hardware. Doesn't need a dedicated instruction unless you're going to get exciting in the program.

Neil

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Well I'm kind of assuming you're emulating|designing|building a complete but minimal processor here, so it would seem that it's just a question of setting a register as part of the reset initialisation: to get the initial reset vector you have to jam the $fffc address onto the bus and then increment it after reading the value into the address register low and high. I don't know what mechanism you would choose to do that, but one could (e.g.)
- tick 0, issue a reset to a register counter
- tick 1, issue a decrement to it
and I feel these could happen in parallel with other required operations for the reset so wouldn't occupy any more time/ticks.

Neil