Extended Z80 instruction set

Standard Z80 Instructions

Register and Data manipulation

LD

The basic data load/transfer instruction. Transfers data from the location specified by the second argument, to the location specified by the first. Available combinations are as follows:

Any 8-bit register can be:
- loaded with an immediate value;
- loaded with the contents of any other 8-bit register except I and R;
- loaded with the contents of, or stored in, memory pointed to by HL;
- loaded with the contents of, or stored in, memory offset-indexed by IX or IY.
Additionally, the accumulator A (only) can be:
- loaded with the contents of, or stored in, memory pointed to by BC or DE;
- loaded with the contents of, or stored in, memory pointed to by an immediate address;
- loaded with the contents of I or R.
Any 16-bit register pair can be:
- loaded with an immediate value;
- loaded with the contents of, or stored in, memory pointed to by an immediate address.
Additionally, SP (only) can be:
- loaded with the contents of HL, IX, or IY.

Although 16-bit register pairs cannot be directly moved between each other, they can be moved by moving the two 8-bit registers. (SP gets a special case because it can't be addressed via 8-bit registers.) Some assemblers will provide built-in macro instructions allowing, for example, ld bc, de.

EX

Exchanges the contents of two sources. The only permitted combinations are

Exchanging DE and HL;
Exchanging AF and AF';
Exchanging HL, IX, or IY with the contents of memory pointed to by SP.

Has no effect on flags (unless AF is exchanged, of course)

EXX: Exchanges BC, DE, and HL with their shadow registers. AF and AF' are not exchanged. Has no effect on flags.

Block Copy

LDI: Copies the byte pointed to by HL to the address pointed to by DE, then adds 1 to DE and HL and subtracts 1 from BC. If BC did not reach 0, P/V is reset, otherwise it is set. H and N are reset.

LDIR: Automatically loops LDI until BC reaches zero. Note that no loop occurs when BC reaches zero.

LDD: Same as LDI, but subtracts 1 from DE and HL instead of adding.

LDDR: Same as LDIR but loops LDD instead of LDI.

Block Search

CPI: Compares the byte pointed to by HL with the contents of A and sets Z if it matches. Then adds 1 to HL and subtracts 1 from BC. Sets P/V if BC did not reach 0 or resets it if it did.

CPIR: Automatically loops CPI until either Z is set (A is found in the byte pointed to by HL) or P/V is reset (BC reached 0).

CPD: Same as CPI, but subtracts 1 from HL instead of adding it.

CPDR: Same as CPIR but loops CPD instead of CPI.

Arithmetic

ADD

Adds values together. Legal combinations are:

When adding 8-bit values the first parameter must be A and the second may be:
- The contents of an 8-bit register;
- An immediate value;
- The contents of memory pointed to by HL or by indexing based on IX or IY.
When adding 16-bit values the first parameter must be HL, IX or IY and the second must be another 16-bit register pair.
On the Spectrum Next the extended Z80 set also allows the first parameter to be HL, DE, or BC and the second to be A.