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Thanks, now it is clear for me (and others). S. [EMAIL PROTECTED] wrote: > This message is from the T13 list server. > > On Mon, 07 Oct 2002 17:30:11 +0200, Stephane Cattaneo wrote: > >This message is from the T13 list server. > >Thanks for your answer. Anyway, let's say that my two devices accept pio mode > >4 (a hdd capable to run up to udma mode 4 and a dvd player capable to run up > >to pio mode 4), so the max speed for pio mode. (this is normally the case for > >all device present in the market). > > In this example you may use PIO mode 4 to talk to both devices (for > both register r/w and for PIO data transfers). The DMA mode of both > device need not match - the HDD can use UltraDMA mode 4 while the DVD > can use MW or UltraDMA (it need not also use UltraDMA mode 4 is the > point). Why is this true? Because when DMACK is asserted by the host > side, the address signals are "disabled" and not used. While DMACK is > asserted the device that is not selected shall ignore the address and > IOR/IOW signals. > > Warning (because if I don't say this Pat will correct me): There are > some *VERY* old devices that do not support DMA and don't even decode > the DMACK signal. These devices may do strange things unless the host > keeps the address signals deasserted while DMACK is assested. This > should not be a problem on any modern host (a host that supports > UltraDMA). > > >Because the commands are sent in pio timings (mode 4 in this case), I think > >that I can communicate in udma mode 4 with the hdd, and pio mode 4 with the > >dvd player. Do you agree that the read and write with the hdd will not > >perturb the dvd player ? > > Yes. > > >Same question when I use the same hdd, plus another hdd capable to run up to > >mode 2 instead of a dvd player. > > In this case you *SHALL* use PIO mode 2 when doing register r/w and > PIO data transfers with both devices. But again if you use DMA with > these two HDD you could use different DMA protocols and/or modes. > > *** Hale Landis *** www.ata-atapi.com ***
