I'm looking through Digikey's Interface - Switches, Multiplexers, Demultiplexers section (and, thanks to W5VO, the Logic - Signal Switches, Multiplexers, Decoders section as well), and I'm having trouble deciphering what circuit/topology I need.
I've got a processor with a 32-bit coprocessor interface, and I'd like to interface it with a parallel Flash or RAM chip. Ideally, I would have both, and could swap between the two in software. I imagined (wrongly, it appears) that this would be a fairly common need, and that I could buy a pair of ICs that would each break out 16 inputs into 2 banks of 16 outputs, with power, ground, a single channel select pin, maybe an enable/high impedance pin. This would ideally come in a 54-pin TSSOP or 64-pin QFP or something of that size. A 32-switch chip would also work, but I imagine that two switches would make routing the a bit easier. The interface would be digital (I don't really need an analog switch), and I'd like to keep up with the 150MHz maximum speed grade of my processor (but will settle for 72MHz or so of actual performance). I am confident that I don't need some of the $200+ crosspoint switches!
I imagined that this would be a simple task, but it seems that my idea of what AxB:C should mean is different from Digikey's idea. I thought that the options would include 1x16:32 or 16x1:2, but (1) these options are not available at reasonable prices (I don't see why this device should cost $70 or $234!), and the other options (like 8x2:1, which seems popular) are designed for analog switching of Ethernet signals.
- Where can I learn about the mux nomenclature? (An answer on this site would be ideal :) Also, where can I learn about the various functions listed, like AV/crosspoint/Ethernet/USB?
- What topology or function should I use for to do this task (digital, ~100MHz, 32 or 16 lines)?
- If all else fails, how can I build a switch out of discrete components or transistor arrays?