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Many thanks for your answers. But why DDMARDY doesn't return to high level before the host has deasserted DMACK- in UDMA data-out mode? -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Mcgrath, Jim Sent: Thursday, January 03, 2002 4:43 AM To: '[EMAIL PROTECTED]'; [EMAIL PROTECTED] Subject: RE: [t13] Ultra DMA query This message is from the T13 list server. The key design principle of UDMA is to have the signals be in the exactly same state after the DMA burst as it was before the DMA burst. Remember that outside of the burst you have to play be old PIO rules, which do not allow for double transitions clocking. It is this careful attention to backward compatibility that makes it so successful. In particular, DSTOBE does not exist outside of a DMA burst. It reverts to the old definition of the signal. HSTROBE is DIOR-, while DSTROBE is IORDY. To make this all work they are in the ASSERTED state when you start a UDMA burst and ASSERTED when you leave the burst. I think 1) was placed there so that if for some reason DSTROBE had not been asserted, the device can assert it. It might be possible that it was deasserted if the last PIO before the UDMA burst was using IORDY. I'd just make sure it is asserted at the start of the burst. In 2) the issue is more straightforward, since if you did not assert it at this point the legacy PIO operations after getting out of UDMA might be strange. Jim -----Original Message----- From: aronlin [mailto:[EMAIL PROTECTED]] Sent: Wednesday, January 02, 2002 1:08 AM To: [EMAIL PROTECTED] Subject: [t13] Ultra DMA query This message is from the T13 list server. Please help me to resolve questions about ultra DMA, 1. During initiating an ulta DMA data-in burst, why need the action, "The device may assert DSTROBE tZIORDY after the host has asserted DMACK-"? does it mean that first strobe should be from high to low? Why? 2. I cannot understand why "if STROBE is not in the asserted state, the sender shall return STROBE to the asserted state" ? STROBE is active on edge not on level, why we have to care its state on high or low? Thanks in advance. Subscribe/Unsubscribe instructions can be found at www.t13.org. Subscribe/Unsubscribe instructions can be found at www.t13.org. Subscribe/Unsubscribe instructions can be found at www.t13.org.
