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Uppermost Page: Difference between revisions
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The '''Uppermost Page''' is the contiguous region of 256 bytes in [[ARAM]] with the highest possible address, located at $FF00. | The '''Uppermost Page''' is the contiguous region of 256 bytes in [[ARAM]] with the highest possible address, located at $FF00. It/offsets within it are abbreviated "upage."<sup>[1]</sup> | ||
[[File:uppermost page.png]] | |||
Both [[TCALL]] and [[PCALL]] utilize it. | |||
The 64-byte [[SPC700/IPL ROM]] lives in the uppermost page at FFC0h.<sup>[2]</sup> But, reading this 64-byte region only returns ROM data when bit 7 of the CONTROL register (00F1h) is set. If bit 7 is clear, then the IPL ROM is currently unmapped, revealing 64 bytes of normal ARAM underneath which will be mapped and read instead. Writes to this 64 byte region always affect the underlying RAM even if CONTROL's bit 7 is set. | |||
=== See Also === | |||
* [[Zero page]] | |||
* [[Direct page]] | |||
=== References === | |||
# [https://archive.org/details/SNESDevManual/book1/page/n226 Appendix C-1 of Book I] of the official Super Nintendo development manual | |||
# [[fullsnes]] | |||
[[Category:ASM]] | [[Category:ASM]] | ||
[[Category:SPC700]] | [[Category:SPC700]] | ||
[[Category:Official Jargon]] | |||
Latest revision as of 11:16, 20 September 2024
The Uppermost Page is the contiguous region of 256 bytes in ARAM with the highest possible address, located at $FF00. It/offsets within it are abbreviated "upage."[1]
Both TCALL and PCALL utilize it.
The 64-byte SPC700/IPL ROM lives in the uppermost page at FFC0h.[2] But, reading this 64-byte region only returns ROM data when bit 7 of the CONTROL register (00F1h) is set. If bit 7 is clear, then the IPL ROM is currently unmapped, revealing 64 bytes of normal ARAM underneath which will be mapped and read instead. Writes to this 64 byte region always affect the underlying RAM even if CONTROL's bit 7 is set.
See Also
References
- Appendix C-1 of Book I of the official Super Nintendo development manual
- fullsnes