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MC68340 データシート(PDF) 90 Page - Freescale Semiconductor, Inc |
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MC68340 データシート(HTML) 90 Page - Freescale Semiconductor, Inc |
90 / 441 page MOTOROLA MC68340 USER’S MANUAL 3- 41 Figure 3-22 is a flowchart showing bus arbitration for a single device. This technique allows processing of bus requests during data transfer cycles. Refer to Figures 3-23 and 3-24 for bus arbitration timing diagrams. BR is negated at the time that BGACK is asserted. This type of operation applies to a system consisting of the MC68340 and one device capable of bus mastership. In a system having a number of devices capable of bus mastership, BR from each device can be wire- ORed to the MC68340. In such a system, more than one bus request could be asserted simultaneously. BG is negated a few clock cycles after the transition of BGACK. However, if bus requests are still pending after the negation of BG, the MC68340 asserts another BG within a few clock cycles after it was negated. This additional assertion of BG allows external arbitration circuitry to select the next bus master before the current bus master has finished using the bus. The following paragraphs provide additional information about the three steps in the arbitration process. Bus arbitration requests are recognized during normal processing, HALT assertion, and a CPU32 halt caused by a double bus fault. GRANT BUS ARBITRATION 1. ASSERT BG TERMINATE ARBITRATION 1. NEGATE BG (AND WAIT FOR BGACK TO BE NEGATED) RE-ARBITRATE OR RESUME PROCESSOR OPERATION PROCESSOR REQUESTING DEVICE REQUEST THE BUS 1. ASSERT BR ACKNOWLEDGE BUS MASTERSHIP 1. EXTERNAL ARBITRATION DETERMINES NEXT BUS MASTER 2. NEXT BUS MASTER WAITS FOR BGACK TO BE NEGATED 3. NEXT BUS MASTER ASSERTS BGACK TO BECOME NEW MASTER 4. BUS MASTER NEGATES BR OPERATE AS BUS MASTER RELEASE BUS MASTERSHIP 1. NEGATE BGACK 1. PERFORM DATA TRANSFERS (READ AND WRITE CYCLES) ACCORDING TO THE SAME RULES THE PROCESSOR USES Figure 3-22. Bus Arbitration Flowchart for Single Request Freescale Semiconductor, Inc. For More Information On This Product, Go to: www.freescale.com |
同様の部品番号 - MC68340 |
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同様の説明 - MC68340 |
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