On Tue, November 30, 2010 4:06 pm, Nate Lawson wrote: > On 11/30/2010 9:54 AM, Jim Brain wrote: >> On 11/30/2010 5:17 AM, Marko Mäkelä wrote: >>> On Tue, Nov 30, 2010 at 11:24:30AM +0100, Niklas Ramsberg wrote: >>>> Is there a single line that can be switched out to make the drive >>>> invisible to the computer? >>> >>> Cutting ATN should do the trick. All communications require ATN to be >>> pulled down by the controller. If the drive always sees ATN=1, it will >>> remain passive. >>> >> Because cbm-hackers is used as a reference resource, I thought I'd add a >> bit, in case someone sees this later and tries to apply it to a >> difference situation. >> >> Cutting ATN does exactly as Marko notes, the drive is "passive". But, >> it is not truly invisible, at least from an electrical perspective. >> >> The other lines (DATA/CLK) are still connected to the bus and loading it >> up (or down, depending on whether the drive is turned on or not). As >> such, if you use such an "ATN-killer" switch on a set of drives, the bus >> could become problematic even though the user thinks many of the devices >> are "invisible". >> >> The cuplrit is the pullup resistors on each drive. When powered, the >> resistors are dragging the lines high. When powered down, they tend to >> drag the line to ground. >> >> For the topic of today (SX-64 drive), it's not a concern, but I thought >> I'd put it out there in case someone gets the impression they can >> connect every drive they own and just mark them "off the bus" by >> switching off ATN. It won't work beyond a certain number of drives (I >> think 8 is probably the limit, at least somewhere around there). > > Jim's analysis is good. I've found that with one drive that is off but > connected to the IEC bus, it doesn't drag the idle level too low (3.3v > high versus 5v). > > But it's better to always operate an IEC bus with all devices powered on > and counting each attached device as a load (even if the device isn't > talking). Don't try more than 4 drives + 1 printer as a max load on a > single bus, and if using more than 2 devices, try to keep the cable > length as short as possible. > And some fast loaders will not function with any other devices on the bus except a single disk drive, correct? - Pete Rittwage C64 Preservation Project Message was sent through the cbm-hackers mailing listReceived on 2010-11-30 22:00:28
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