| R (Memory Refresh) || 8-bit || Increments after each M1 cycle (instruction or prefix fetch) to refresh DRAM || Only the lower 7 bits are incremented. Bit7 can only be changed by writing to the R register.
|}
See: [https://www.righto.com/2014/10/how-z80s-registers-are-implemented-down.html How the Z80's registers are implemented]
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