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 Post subject: 74HC161 as a switch?
PostPosted: Wed Oct 17, 2018 4:13 pm 
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Joined: Wed Feb 15, 2012 10:19 pm
Posts: 86
Can I use a PC74HC161P as a switch to either ground one board or another? If so, how would i wire it? Switch one on and the other off when there is a reset.


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 Post subject: Re: 74HC161 as a switch?
PostPosted: Wed Oct 17, 2018 4:25 pm 
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Joined: Sun Apr 13, 2008 11:12 am
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Location: Seattle
Not by itself, no. You'll need some other part to convert the output from the counter into something that only enables one ROM or another.


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 Post subject: Re: 74HC161 as a switch?
PostPosted: Wed Oct 17, 2018 5:45 pm 
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Joined: Tue Aug 28, 2018 8:54 am
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Location: Edmonton, Canada
You can use multiplexer/demultiplexer for that. You should be able to wire both roms on one address bus, and use 8-16 bit multiplexer to choose data bus.


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 Post subject: Re: 74HC161 as a switch?
PostPosted: Thu Oct 18, 2018 11:26 am 
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Joined: Wed Feb 15, 2012 10:19 pm
Posts: 86
I have some 74LS139. Could they be used to make a switch or in combination?


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 Post subject: Re: 74HC161 as a switch?
PostPosted: Thu Oct 18, 2018 11:43 am 
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Joined: Sun Apr 13, 2008 11:12 am
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Location: Seattle
Sure, in combination.

Details depend on exact details of what you're trying to do (e.g. one PCB with multiple ROMs, multiple preexisting PCBs, &c)


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 Post subject: Re: 74HC161 as a switch?
PostPosted: Thu Oct 18, 2018 11:49 am 
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Joined: Wed Feb 15, 2012 10:19 pm
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I wanted to wire 2 gameboy games to a super gameboy board and use the ground to select which one plays or that what I thought would work.


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 Post subject: Re: 74HC161 as a switch?
PostPosted: Thu Oct 18, 2018 12:11 pm 
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Joined: Sun Apr 13, 2008 11:12 am
Posts: 7817
Location: Seattle
Use the 74'139 as:

1- from the SGB, connect A15 ("/LOSEL") and /CS ("/HISEL") to the two half '139's /E inputs
2- from the counter, connect QA (the least significant bit output) to the two half '139's A inputs
3- from the '139, connect the /Y0 outputs to A15 and /CS on one cart, and the /Y1 outputs to the other cart

Configure the 74'161 to count up by one whenever the /RESET signal goes low


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