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DP8390D Datasheet(PDF) 36 Page - National Semiconductor (TI) |
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DP8390D Datasheet(HTML) 36 Page - National Semiconductor (TI) |
36 / 56 page 130 Bus Arbitration and Timing (Continued) REMOTE READ TIMING 1) The DMA reads byteword from local buffer memory and writes byteword into latch increments the DMA address and decrements the byte count (RBCR01) 2) A Request Line (PRQ) is asserted to inform the system that a byte is available 3) The system reads the port the read strobe (RACK)is used as an acknowledge by the Remote DMA and it goes back to step 1 Steps 1 – 3 are repeated until the remote DMA is com- plete Note that in order for the Remote DMA to transfer a byte from memory to the latch it must arbitrate access to the local bus via a BREQ BACK handshake After each byte or word is transferred to the latch BREQ is dropped If a Local DMA is in progress the Remote DMA is held off until the local DMA is complete TLF8582 – 72 REMOTE WRITE TIMING A Remote Write operation transfers data from the IO port to the local buffer RAM The NIC initiates a transfer by re- questing a byteword via the PRQ The system transfers a byteword to the latch via IOW this write strobe is detected by the NIC and PRQ is removed By removing the PRQ the Remote DMA holds off further transfers into the latch until the current byteword has been transferred from the latch PRQ is reasserted and the next transfer can begin 1) NIC asserts PRQ System writes byteword into latch NIC removes PRQ 2) Remote DMA reads contents of port and writes byteword to local buffer memory increments address and decrements byte count (RBCR01) 3) Go back to step 1 Steps 1 – 3 are repeated until the remote DMA is com- plete TLF8582 – 73 36 |
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