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 ***
