Accumulator or A register is an 8-bit register used for arithmetic, logic, I/O and load/store operations.
Flag is an 8-bit register containing 5 1-bit flags:
- Sign - set if the most significant bit of the result is set.
- Zero - set if the result is zero.
- Auxiliary carry - set if there was a carry out from bit 3 to bit 4 of the result.
- Parity - set if the parity (the number of set bits in the result) is even.
- Carry - set if there was a carry during addition, or borrow during subtraction/comparison.
General registers:
- 8-bit B and 8-bit C registers can be used as one 16-bit BC register pair. When used as a pair the C register contains low-order byte. Some instructions may use BC register as a data pointer.
- 8-bit D and 8-bit E registers can be used as one 16-bit DE register pair. When used as a pair the E register contains low-order byte. Some instructions may use DE register as a data pointer.
- 8-bit H and 8-bit L registers can be used as one 16-bit HL register pair. When used as a pair the L register contains low-order byte. HL register usually contains a data pointer used to reference memory addresses.
Stack pointer is a 16 bit register. This register is always incremented/decremented by 2.
Program counter is a 16-bit register.
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