On Sun, 25 Feb 101 email@example.com wrote: > Hallo Nick, > > > >Yes. But also tristates the address- and databus. And that is something > > that > > >does not happen with the PC-bus. And I'm very sure not even wanted. > > > That's right, you don't want it... then 8237DMA controller is on the PC > > mainboard and though the CPU is tri-stated, it controls read/writes > > from/to IO/MEM.... if the concept is to have a PC card plug into the C64, > > then someone has to be awake to make the transfer else a DMA controller > > will be needed between the two. > > I'm sorry, either you do not understand it, or I don't understand what you > wrote. So for sure I repeat everything: > - the IOCKRDY line is to halt the CPU and nothing more. The CPU stops > processing but address- and databus reamin active. My comment was that the IOCKRDY is not used for dma. Its for stallin ghte cpu for slow devices. > 6502 has this feature as well. But the trouble was that this input could > not be used as it was not connected to the expansionbus. > Marko commented to use the DMA-input which resulted into my comment that > this input could _NOT_ be used as using this input would not only result in > stopping the CPU but also tristating the address-and databus. The IOCKRDY > input was meant to be used by slow memory or I/O. You surely don't help the > poor slow device by tristating the databus during a read.... > > As I understand, you say that we need a DMA controller before we can use a > PC card? Why? The MGP card for example does not use DMA. And As I already If your target card doesnt use dma, you dont need a dmac. > said, it run fine with my C64 from 1989 on. DMA is only needed with > floppies, harddisks and networkcards, at least for the PC. I already proved > that the C64 doesn't need one for a IDE-disk (OK, speed is not "je-van-het" > but...). I don't see any reason why it should not work for a 360KB floppy, > for the 1.44 I have my doubts. The FDC does use dma, but it doesnt need to. Again, I recommend using dma whenever possible. :) UHS (my scsi project, see http://uhs.c64.org ) will have to deal with the PC-DMA->c64 issue. i've decided to either make a very simple DMAC or use an 8237a and allow others to use the remaining 3 dma channels via a shortbus-style cabling setup. Side note: I'm working on matchign ISA signals with the c64's bus (as well as what I blieve is likely on the supercpu's ram socket), so that one can use an ISA bus with thet c64 and/or scpu. This involves having just a PIC and DMAC set, and no other chipset involved. There would be no x86 cpu on the bus, which means it would require a passive backplane. COnveniently enough, the local junk store has 7slot backplanes for $5 each ;) comments? - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail firstname.lastname@example.org.
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