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Contended I/O: Difference between revisions
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m (IO → I/O as per Zilog Z80 and Spectrum BASIC manuals and Wikipedia) |
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# If the port address has its low bit reset, the ULA pauses the processor by stopping its clock. | # If the port address has its low bit reset, the ULA pauses the processor by stopping its clock. | ||
# If the port being accessed is between 0x4000 and 0x7fff, this "looks like" an access to contended memory to the ULA and it again pauses the processor by stopping its clock. Contention is also applied if the port address is between 0xc000 and 0xffff on a 128K Spectrum with a contended RAM bank paged into that address range.<ref> | # If the port being accessed is between 0x4000 and 0x7fff, this "looks like" an access to contended memory to the ULA and it again pauses the processor by stopping its clock. Contention is also applied if the port address is between 0xc000 and 0xffff on a 128K Spectrum with a contended RAM bank paged into that address range.<ref>https://www.worldofspectrum.org/forums/showpost.php?p=215386&postcount=88</ref><ref>https://www.worldofspectrum.org/forums/showthread.php?t=18214</ref> | ||
The combination of these two effects leads to the following pattern: | The combination of these two effects leads to the following pattern: | ||