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Z80 CPU Instructions UM008007-0715

Z80 CPU

User Manual

Descriptions of the 16-Bit Load Group instructions begin on page 96.

These 16-bit load operations differ from other 16-bit loads in that the stack pointer is auto-

matically decremented and incremented as each byte is pushed onto or popped from the

stack, respectively. For example, the PUSH AF instruction is a single-byte instruction with

the op code of

F5h. During execution, this sequence is generated as:

Decrement SP

LD (SP), A

Decrement SP

LD (SP), F

The external stack now appears as shown in Figure 36.

The POP instruction is the exact reverse of a PUSH. All PUSH and POP instructions uti-

lize a 16-bit operand and the high-order byte is always pushed first and popped last.

PUSH BC is PUSH 8 then C

PUSH DE is PUSH D then E

PUSH HL is PUSH H then L

POP HL is POP L then H

The instruction using extended immediate addressing for the source requires two bytes of

data following the op code, as shown in the following example:

LD DE, 0659h

The instruction sequence for this value in memory is shown in Figure 37.

Figure 36. Example of a 16-Bit Load Operation

Note:

(SP)

(SP+1)

Top of stack

•

1 2 ... 51 52 53 54 55 56 57 58 59 60 61 ... 325 326

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