View source for CPU Registers and Flags

===Registers===

  16bit Hi   Lo   Name/Function
  AF    A    -    Accumulator & Flags
  BC    B    C    BC
  DE    D    E    DE
  HL    H    L    HL
  SP    -    -    Stack Pointer
  PC    -    -    Program Counter/Pointer

As shown above, most registers can be accessed either as one 16bit register, or as two separate 8bit registers.

===The Flag Register (lower 8bit of AF register)===

  Bit  Name  Set Clr  Expl.
  7    zf    Z   NZ   Zero Flag
  6    n     -   -    Add/Sub-Flag (BCD)
  5    h     -   -    Half Carry Flag (BCD)
  4    cy    C   NC   Carry Flag
  3-0  -     -   -    Not used (always zero)

Conatins the result from the recent instruction which has affected flags.

===The Zero Flag (Z)===
This bit becomes set (1) if the result of an operation has been zero (0). Used for conditional jumps.

===The Carry Flag (C, or Cy)===
Becomes set when the result of an addition became bigger than FFh (8bit) or FFFFh (16bit). Or when the result of a subtraction or comparision became less than zero (much as for Z80 and 80x86 CPUs, but unlike as for 65XX and ARM CPUs). Also the flag becomes set when a rotate/shift operation has shifted-out a "1"-bit.
Used for conditional jumps, and for instructions such like ADC, SBC, RL, RLA, etc.

===The BCD Flags (N, H)===
These flags are (rarely) used for the DAA instruction only, N Indicates whether the previous instruction has been an addition or subtraction, and H indicates carry for lower 4bits of the result, also for DAA, the C flag must indicate carry for upper 8bits.
After adding/subtracting two BCD numbers, DAA is intended to convert the result into BCD format; BCD numbers are ranged from 00h to 99h rather than 00h to FFh.
Because C and H flags must contain carry-outs for each digit, DAA cannot be used for 16bit operations (which have 4 digits), or for INC/DEC operations (which do not affect C-flag).