On 11/1/2017 3:24 AM, Mia Magnusson wrote: > Den Tue, 31 Oct 2017 23:08:14 -0500 skrev Jim Brain <brain@jbrain.com>: >> On 10/31/2017 3:02 AM, Mia Magnusson wrote: >>> Sorry if this is an old topic. >>> >>> Are there any schematics available for Handic VIC-Switch, or some >>> similar device? >> http://jbrain.com/pub/cbm/hw/VICSwitch/VICSwitch.sch > Thank you very much! > > So what it basically does is that it uses a 3 bit counter that selects > each computer connector and as soon as it finds a computer pulling ATN > it holds the counter until ATN is released, while the 74138 and 7405 > holds DAT low on each not selected computer. Quite clever! I think there is a timer that holds the line low for a bit after the ATN goes high., as ATN is only low while the IEC "command" is sent, not the data. > > I'm not that familiar with burst mode. Would an additional (or actually > two in parallell) 4051 for SRQ be enough? As previously response notes, no, it is not that easy (and, you are correct, it's a pair of 4051s to add, not a '151 as I stated in my last email). > > How does this play with disk turbos? AFAIK they use CLK and DAT as two > data lines so would probably work through this device. 2 lines would be OK, as the system makes very few assumptions on the two lines (though, the reason 2 line fastloaders are 2 line fastloaders is that they obey the first part of the IEC protocol, and don't use ATN line so they can work on the shared bus. As a result, the command usage ona 2 line fastloader should obey all of the same rules the VIC-Switch obeys (DAT line low on ATN low, etc.) > > -- Jim Brain brain@jbrain.com www.jbrain.com Message was sent through the cbm-hackers mailing listReceived on 2017-11-01 15:00:02
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