Ez80® cpu instruction notations, Ez80, Cpu instruction notations – Zilog EZ80F916 User Manual
Page 62
eZ80
®
CPU
User Manual
UM007715-0415
CPU Instruction Set
53
description of instruction operands. The nomenclature is defined with special emphasis on
mnemonic values and readability.
The movement of data is indicated by a single opcode, regardless whether the movement
is between different registers or between registers and memory locations. For example, the
first operand of an LD instruction is the destination of the operation and the second
operand is the source of the operation. Thus, LD A, B indicates that the contents of the
second operand, working register B, are to be transferred to the first operand, which is the
accumulator, A. In the opcode descriptions, this operation is often represented as:
A
B
Similarly, LD C,
3Fh
indicates that the constant
3Fh
is written to working register C:
C
3Fh
Enclosing an operand in parentheses indicates a memory location addressed by the
contents of the parentheses (i.e. an indirect memory access). For example, LD BC, (HL)
indicates that the contents of the multibyte HL register are used as an address to a memory
location. Multi-byte register BC is loaded with the data stored at the memory location
pointed to by the contents of HL:
BC
(HL)
Similarly, LD (IX+6), C indicates that the contents of register C are to be stored in the
memory location addressed by the current value in the multibyte IX register plus 6:
(IX+6)
C
eZ80
®
CPU Instruction Notations
The notations in the CPU instructions are defined in
Table 26. Instruction Notations
Mnemonic
Definition
cc
Condition code C, NC, Z, NZ, P, M, PO, or PE—tests of
single bits in Flags register
cc’
Condition code C, NC, Z, or NZ—tests of single bits in
Flags register
d
An 8-bit two’s complement displacement with value from
–128 to 127
ir
or ir’
8-bit CPU register IXH (IX[15:8]), IXL (IX[7:0]), IYH
(IY[15:8]), or IYL (IY[7:0])
IX/Y
CPU Index Register IX or IY
(IX/Y+d)
A location in memory with address formed by the sum of
the contents of the Index Register, IX or IY, and the two’s-
complement
displacement
d