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Excerpts for 116B (224KB)
Excerpts for 116B (224KB)
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2.2.5 Address Register Indirect with Predecrement Mode<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. Be<strong>for</strong>e 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 <strong>for</strong> 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 />
.<br />
GENERATION:<br />
ASSEMBLER SYNTAX:<br />
EA MODE FIELD:<br />
EA REGISTER FIELD:<br />
NUMBER OF EXTENSION WORDS:<br />
EA = (An)–SIZE<br />
– (An)<br />
100<br />
REG. NO.<br />
0<br />
31<br />
0<br />
ADDRESS REGISTER<br />
CONTENTS<br />
OPERAND LENGTH ( 1, 2, OR 4)<br />
SIZE<br />
OPERAND POINTER<br />
31<br />
CONTENTS<br />
0<br />
POINTS TO<br />
MEMORY<br />
OPERAND<br />
MOTOROLA M68000 FAMILY PROGRAMMER’S REFERENCE MANUAL 2-7