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M68000 Microprocessor User's Manual

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BUS MASTER<br />

ADDRESS THE DEVICE<br />

1) SET R/W TO READ<br />

2) PLACE FUNCTION CODE ON FC2–FC0<br />

3) PLACE ADDRESS ON A23–A1<br />

4) ASSERT ADDRESS STROBE (AS)<br />

5) ASSERT UPPER DATA STROBE (UDS)<br />

AND LOWER DATA STROBE (LDS)<br />

ACQUIRE THE DATA<br />

SLAVE<br />

INPUT THE DATA<br />

1) DECODE ADDRESS<br />

2) PLACE DATA ON D15–D0<br />

3) ASSERT DATA TRANSFER<br />

ACKNOWLEDGE (DTACK)<br />

1) LATCH DATA<br />

2) NEGATE UDS AND LDS<br />

3) NEGATE AS<br />

TERMINATE THE CYCLE<br />

1) REMOVE DATA FROM D15–D0<br />

2) NEGATE DTACK<br />

START NEXT CYCLE<br />

Figure 5-1. Word Read-Cycle Flowchart<br />

BUS MASTER<br />

ADDRESS THE DEVICE<br />

1) SET R/W TO READ<br />

2) PLACE FUNCTION CODE ON FC2–FC0<br />

3) PLACE ADDRESS ON A23-A1<br />

4) ASSERT ADDRESS STROBE (AS)<br />

5) ASSERT UPPER DATA STROBE (UDS)<br />

OR LOWER DATA STROBE (LDS)<br />

(BASED ON INTERNAL A0)<br />

ACQUIRE THE DATA<br />

SLAVE<br />

INPUT THE DATA<br />

1) DECODE ADDRESS<br />

2) PLACE DATA ON D7–D0 OR D15–D8<br />

(BASED ON UDS OR LDS)<br />

3) ASSERT DATA TRANSFER<br />

ACKNOWLEDGE (DTACK)<br />

1) LATCH DATA<br />

2) NEGATE UDS AND LDS<br />

3) NEGATE AS<br />

TERMINATE THE CYCLE<br />

1) REMOVE DATA FROM D7–D0<br />

OR D15–D8<br />

2) NEGATE DTACK<br />

START NEXT CYCLE<br />

Figure 5-2. Byte Read-Cycle Flowchart<br />

5- 2 <strong>M68000</strong> 8-/16-/32-BIT MICROPROCESSORS USER'S MANUAL MOTOROLA

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