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H8SX/1663R 数据表(PDF) 551 Page - Renesas Technology Corp |
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H8SX/1663R 数据表(HTML) 551 Page - Renesas Technology Corp |
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551 / 1504 page  Section 11 EXDMA Controller (EXDMAC) Rev. 2.00 Sep. 24, 2008 Page 519 of 1468 REJ09B0412-0200 (5) EDREQ Pin Low Level Activation Timing with NRD = 1 Specified When the NRD bit is set to 1 in EDMDR, the acceptance timing of the next transfer request can be delayed one cycle later. Figure 11.38 shows an example of single address mode transfer activated by the EDREQ pin low level with NRD = 1 specified. EDREQ pin sampling is performed in each cycle starting at the next rise of Bφ after the end of the DTE bit write cycle. When a low level is sampled at the EDREQ pin while acceptance of a transfer request via the EDREQ pin is possible, the request is held within the EXDMAC. Then when activation is initiated within the EXDMAC, the request is cleared. After the end of the single cycle, acceptance resumes when one cycle of the request clearance period specified by NRD = 1 expires and EDREQ pin low level sampling is performed again. This sequence of operations is repeated until the end of the transfer. Minimum 3 cycles Minimum 3 cycles EXDMA single EXDMA single B φ EDREQ Address bus Channel [1] [2] [3] [4] [5] [6] [7] [1] Acceptance after transfer enabling; EDREQ pin low level is sampled at rise of Bφ, and request is held. [2], [5] Request is cleared at end of next bus cycle, and activation is started in EXDMAC. [3], [6] EXDMA cycle starts. [4], [7] Acceptance is resumed after completion of write cycle plus one cycle. (As in [1], EDREQ pin low level is sampled at rise of Bφ, and request is held.) Bus release Bus release Acceptance resumed Acceptance resumed Request Request Request clearance period Request clearance period Bus release Extended request clearance period specified by NRD Extended request clearance period specified by NRD Transfer source/ Transfer destination Transfer source/ Transfer destination Figure 11.38 Example of Single Address Mode Transfer Activated by EDREQ Pin Low Level with NRD = 1 Specified |
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