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MOTOROLA M68000 FAMILY Programmer's Reference ... - Freescale

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2.2.5 Address Register Indirect with Predecrement Mode<br />

<strong>MOTOROLA</strong><br />

<strong>M68000</strong> <strong>FAMILY</strong> PROGRAMMER’S REFERENCE MANUAL<br />

Addressing Capabilities<br />

In the address register indirect with predecrement mode, the operand is in memory. The<br />

effective address field specifies the address register containing the address of the operand<br />

in memory. Before the operand address is used, it is decremented by one, two, or four<br />

depending on the operand size: byte, word, or long word, respectively. Coprocessors may<br />

support decrementing for any operand size up to 255 bytes. If the address register is the<br />

stack pointer and the operand size is byte, the address is decremented by two to keep the<br />

stack pointer aligned to a word boundary.<br />

GENERATION:<br />

ASSEMBLER SYNTAX:<br />

EA MODE FIELD:<br />

EA REGISTER FIELD:<br />

NUMBER OF EXTENSION WORDS:<br />

ADDRESS REGISTER<br />

OPERAND LENGTH ( 1, 2, OR 4)<br />

OPERAND POINTER<br />

EA = (An)–SIZE<br />

– (An)<br />

100<br />

REG. NO.<br />

0<br />

.<br />

31<br />

31<br />

SIZE<br />

CONTENTS<br />

CONTENTS<br />

POINTS TO<br />

MEMORY OPERAND<br />

0<br />

0<br />

2-7

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