The comp.sys.sinclair FAQ contains detailed information on the Spectrum 128, but contains a number of errors/omissions:
- Reading from port 0x7ffd does produce an effect: the value read (generally the floating bus value) is written back to port 0x7ffd. (This effect does not occur on the +2A/+3).
- Contended IO does apply to ports in the range 0xc000 to 0xffff if a contended memory page is currently paged in.
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