6510 question

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Gyro Gearloose
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6510 question

Post by Gyro Gearloose »

Since the 6510 uses addresses $0000 and $0001 for the 6 pin I/O port built into the chip, do accesses to these two addresses cause external changes on the external 6510 address and data lines?

Like does reading or writing to these addresses generate a R/W cycle with the data ignored by the CPU? Does writing to $0001 also write to RAM?


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merman
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Re: 6510 question

Post by merman »

The RAM location mirrors the data lines. So POKEing or storing to the RAM location (usually best with interrupts disabled) will change the data line, while PEEKing or loading from the RAM location returns the current setting of the data lines.
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Gyro Gearloose
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Re: 6510 question

Post by Gyro Gearloose »

Not sure I understand your reply. Locations $0000 and $0001 in the 6510 are mapped internally to the I/O port. Do accesses to those addresses generate external CPU bus cycles?

In any case it means that if you map the VIC-II to the first 16K, the 6510 can only write 16382 bytes there.

I feel cheated.
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Re: 6510 question

Post by Gyro Gearloose »

Just some more idle speculation: I guess the only way to really read and write to RAM at locations $0000 and $0001 is with an REU or something external that does DMA?

Just curious... Of course this makes me wonder how things like a SuperCPU can access the 6510's port? Is there something to let the 6510 execute instructions accessing $0000 and $0001? And how does the 6510 hand back control after? Must be a software trick to do that somehow.
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