Re: Bus Timing on C64: Thanks
                                       
   From: John Iannetta <73510.2152@CompuServe.COM>
   Reply to: John Iannetta
   Date: Tue, 01 Dec 1998 18:16:03 -0500
   Organization: CompuServe, Inc. (1-800-689-0736)
   References:
          <73vknl$d75$1@nnrp1.dejanews.com>
    Ash said,

"When writing back to the bus (read cycle) do I need to consider the bus
available line or is it only needed for DMA type applications ?".

    You can ignore BA, as long as you are using the 6510 MPU.  Every eight
scanning lines, VIC (the 6567/6569) will take BA low for 43 clock cycles,
temporarily stopping the 6510.  But it picks up where it left off, so it
doesn't know that it was idle for those cycles.  Unless, of course, you are
using a software delay or such.

    When using an external MPU, a DMA is done by taking one input of a 2-input
OR gate low.  The other input is the phase 2 line (pin E of the cartridge
port); the output goes to -DMA (pin 13 of the cartridge port).  That will stop
the 6510, and also take AEC low (tri-stating the 6510's address bus, data bus,
and R/-W line).

--
I pressed RETURN, and the message said, "Missing GOSUB".

                          John