Kirk Wallace wrote: > This link: > http://www.beyondlogic.org/epp/epp.htm > > seems to indicate that one only needs to do a write to the EPP Data or > Address register to do an EPP transfer. There doesn't seem to means to > "put" the card into EPP mode. What am I missing? > > A write of 0x80 to the address 0x402 above the data register (default 0x378) sets a parallel port with standard register assignment to EPP mode. Many chips do this, but not all follow the standard. > Bi-directional SPP seems to be the most reliable since the driver has > access to the entire transfer process. It is slower, but it might be > fast enough for many applications. > Way slower. A faster EPP chip can do a complete byte transfer in 400 ns to one of my boards. Other EPP chips do it in 600 - 800 ns, even the old ISA compatible chips on 1998 Dell motherboards.
Emulating the full EPP handshake requires writing data to the port and setting the WRITE/ signal, then asserting DATA_STROBE/, waiting for WAIT, deasserting DATA_STROBE/ and waiting for WAIT to go away. At the least, that's 5 transfers between CPU and the parport chip, so about 2 us, maybe. You could still control one of my boards this way, but the overhead would be quite a bit more. If we ever get RTAI running on the Beagle Board, the control of the parallel port will look quite a bit like this. Jon ------------------------------------------------------------------------------ Special Offer-- Download ArcSight Logger for FREE (a $49 USD value)! Finally, a world-class log management solution at an even better price-free! Download using promo code Free_Logger_4_Dev2Dev. Offer expires February 28th, so secure your free ArcSight Logger TODAY! http://p.sf.net/sfu/arcsight-sfd2d _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
