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H8SX1663 数据表(PDF) 346 Page - Renesas Technology Corp |
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H8SX1663 数据表(HTML) 346 Page - Renesas Technology Corp |
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346 / 1158 page ![]() Section 6 Bus Controller (BSC) Rev.1.00 Jun. 07, 2006 Page 294 of 1102 REJ09B0294-0100 (2) Write after Read If an external write occurs after an external read while bit IDLS0 in IDLCR is set to 1, idle cycles specified by bits IDLCA1 and IDLCA0 when bit IDLSELn in IDLCR is cleared to 0 when IDLSELn = 0, or bits IDLCB1 and IDLCB0 when IDLSELn is set to 1 are inserted at the start of the write cycle (n = 0 to 7). Figure 6.91 shows an example of the operation in this case. In this example, bus cycle A is a read cycle for ROM with a long output floating time, and bus cycle B is a CPU write cycle. In (a), an idle cycle is not inserted, and a conflict occurs in bus cycle B between the read data from ROM and the CPU write data. In (b), an idle cycle is inserted, and a data conflict is prevented. Data hold time is long. Data conflict Bus cycle A Bus cycle B B φ Address bus CS (area A) CS (area B) RD LLWR Data bus T 1 T 2 T 3 T 1 T 2 (b) Idle cycle inserted Bus cycle A Bus cycle B T 1 T 2 T 3 T 1 T i T 2 (a) No idle cycle inserted (IDLS0 = 0) (IDLS0 = 1, IDLSELn = 0, IDLCA1 = 0, IDLCA0 = 0) Figure 6.91 Example of Idle Cycle Operation (Write after Read) |
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