Bit Operations and the Index Registers

Abstract

The Z80 has an extensive range of bit instructions. The bit instructions allow individual bits of a register or memory byte to be tested (for 0 or 1), set to 1 and reset to 0. The number of the bit in the register or memory byte to be used in the operation has to be specified in the instruction and, for this purpose, the bits are numbered right to left starting at 0, as follows

All bit instructions operate on any of one of the single registers or a memory byte pointed to by HL, IX or IY.