Nitro2k01 at 02:21, 5 April 2020

2020-04-05T02:21:14Z

Xzakox at 12:58, 28 June 2009

2009-06-28T12:58:18Z

Xzakox: New page: ===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 ...

2009-06-28T10:55:25Z

New page: ===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 ...

New page

===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).

← Older revision		Revision as of 02:21, 5 April 2020
Line 1:		Line 1:
−	{{Pandocs\|~~cpuregistersandflags~~}}	+	{{Pandocs\|registers-and-flags}}

	===Registers===		===Registers===

← Older revision		Revision as of 12:58, 28 June 2009
Line 1:		Line 1:
		+	{{Pandocs\|cpuregistersandflags}}
		+
	===Registers===		===Registers===

CPU Registers and Flags - Revision history

Nitro2k01 at 02:21, 5 April 2020

Xzakox at 12:58, 28 June 2009

Xzakox: New page: ===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 ...