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- Contended memory is Sinclair's name for a portion of the ZX Spectrum's 64 KB addressable memory space. With the full 64 KB, the Z80 microprocessor is the exclusive bus master, so it reads and writes operate at its full bus speed, but contended memory space is shared between the ULA and the Z80, with the ULA having higher priority. Contended memory occupies addresses 0x4000..0x7FFF of the Z80 memory map. This is the first 16 KB of RAM in the 48 KB machine and the entire RAM of the 16 KB machine. Contention occurs as a result of the ULA reading the display and attributes data in this RAM to produce the TV video display. Contention therefore does not occur during horizontal flyback, vertical flyback or during the screen border. Accesses to I/O also contend if the ULA must read contended memory while the Z80 accesses a ULA I/O port. ULA I/O ports are those with an even address (address bit 0 is a 0). The Z80 must wait whenever the ULA needs to access contended memory before proceeding with its own contended memory read or write. The effect to the user is that programs that make use of contended memory or contended I/O run slower than those that avoid it. (en)
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- Contended memory is Sinclair's name for a portion of the ZX Spectrum's 64 KB addressable memory space. With the full 64 KB, the Z80 microprocessor is the exclusive bus master, so it reads and writes operate at its full bus speed, but contended memory space is shared between the ULA and the Z80, with the ULA having higher priority. Contended memory occupies addresses 0x4000..0x7FFF of the Z80 memory map. This is the first 16 KB of RAM in the 48 KB machine and the entire RAM of the 16 KB machine. (en)
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