Appendix 7 — Addressing, Prefixes and Forms

---

Addressing Shapes

Shape	Example	Meaning	Typical use
immediate byte	ld a, $2A	constant encoded in the instruction	constants, masks, small values
immediate word	ld hl, $8000	16-bit constant encoded in the instruction	addresses, counters, setup
register	ld d, a	copy between registers	cheap data movement
register pair	add hl, de	operate on a 16-bit pair	addresses, word arithmetic
register indirect	ld a, (hl)	memory at address in HL	pointer-based table walk
indexed indirect	ld a, (ix+3)	memory at IX + displacement	records, stack frames
absolute memory	ld a, ($8000)	memory at a fixed 16-bit address	globals, I/O-mapped data
relative branch	jr nz, loop	branch by signed offset	short local branches
absolute branch	jp nz, target	branch to full 16-bit address	long-range control flow

---

Prefix Families

Prefix	Family	What it usually means
none	base	ordinary documented Z80 instruction set
CB	rotate/shift/bit family	RLC, BIT, RES, SET, and friends
ED	extended family	block ops, NEG, RETI/RETN, IM, RLD/RRD, 16-bit ADC/SBC, port forms
DD	IX substitution	many HL-based forms become IX-based
FD	IY substitution	many HL-based forms become IY-based
DD CB d	indexed bit/shift family	operate on (IX+d)
FD CB d	indexed bit/shift family	operate on (IY+d)

DD and FD do not magically legalise every HL instruction.

---

LD Quick Table

Family	Examples	Notes
8-bit register to register	ld a, b, ld d, h	common and fast
immediate to register	ld a, $2A, ld hl, $8000	constants encoded in instruction
register with (HL)	ld a, (hl), ld (hl), a, ld (hl), 0	main indirect byte access
register with (IX+d) / (IY+d)	ld a, (ix+3), ld (iy-1), a	indexed access
A with (BC) / (DE)	ld a, (bc), ld (de), a	only A is allowed
absolute memory	ld a, ($8000), ld ($8000), a, ld hl, ($8000)	globals and fixed addresses
stack pointer load	ld sp, hl, ld sp, ix, ld sp, iy	special-case form

Illegal pattern to remember:

ld ($8001), ($8000)   ; impossible

Memory-to-memory moves must go through a register.

---

Arithmetic, Logic, and Compare Quick Table

Family	Main forms	Result goes to	Notes
ADD	add a,x, add hl,ss, add ix,pp, add iy,rr	first operand	8-bit add is accumulator-based
ADC	adc a,x, adc hl,ss	first operand	includes carry
SUB	sub x	A	accumulator only
SBC	sbc a,x, sbc hl,ss	first operand	subtract with carry/borrow
AND	and x	A	accumulator only
OR	or x	A	accumulator only
XOR	xor x	A	accumulator only
CP	cp x	no stored result	flags only
INC	inc r, inc rr, inc (hl), inc (ix+d)	operand itself	changes the operand in place
DEC	dec r, dec rr, dec (hl), dec (ix+d)	operand itself	often used for loops

---

Rotate, Shift, and Bit Quick Table

Family	Examples	Notes
accumulator rotates	rlca, rrca, rla, rra	short one-byte accumulator forms
general rotates	rlc r, rrc r, rl r, rr r	base CB family
shifts	sla r, sra r, srl r	base CB family
bit test	bit n,r, bit n,(hl)	tests a bit and leaves the operand as it stands
bit clear	res n,r, res n,(hl)	writes back changed value
bit set	set n,r, set n,(hl)	writes back changed value
indexed forms	bit 3,(ix+2), srl (iy-1)	DD CB d / FD CB d families
classic-undocumented shift	sll r / sls r	widely used but not part of the original documented set

---

Control Flow, Stack, and Exchange Quick Table

Family	Examples	Notes
absolute jump	jp target, jp nz,target, jp (hl)	long-range branch
relative jump	jr target, jr z,target	short branch only
counted branch	djnz loop	B := B - 1, branch if result not zero
call/return	call fn, ret, ret z	uses hardware stack
restart	rst $38	call to fixed low-memory vector
stack	push bc, pop hl	word-sized only
exchange	ex de,hl, ex af,af', exx, ex (sp),hl	swaps rather than copies
interrupt state	di, ei, im 0/1/2	machine control, not everyday data movement

---

Block Instructions At A Glance

Family	Mnemonics	What they do
block transfer	LDI, LDIR, LDD, LDDR	copy bytes between (HL) and (DE) while updating pointers/counter
block compare	CPI, CPIR, CPD, CPDR	compare A against bytes in memory while updating pointers/counter
block input	INI, INIR, IND, INDR	port input plus memory store
block output	OUTI, OTIR, OUTD, OTDR	memory read plus port output