Bus mastering, a feature supported by many bus architectures that enables a device connected to the bus to initiate transactions.
Compared to the unified system and video memory used by other 8-bit computers of the time, such as the Apple II, ZX Spectrum, and Commodore 64, separate memory has the advantage of freeing up of the Z80 processor's 64 KiB address space for main RAM, and the VDP doesn't need to steal CPU cycles to access video memory.
If there is no device that implements the function zero (i.e., vendor and device ID registers), the bus master performs an abort and returns all 1s in binary (hexadecimal FFFFFFFF).
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