Hi all, I'm looking for recommendations for suitable 2:1 multiplexers. The 74157 only takes two 4-bit inputs. I'm after something that can take two 8-bit inputs, and also two 16-bit inputs. I know I can just use multiple 74157s, I'm just trying to minimize chip count and wiring.

I haven't been able to find any 8-bit 2:1 digital multiplexers. I have found some 8-bit 2:1 analog multiplexers such as the IDT74FST32390Q (now obsolete?). Does anybody have experience using analog multiplexers in digital design? Can they also be used as demultiplexers?

I'm after a DIP package solution as I'm doing a breadboard design (very slow clock rate, < 1kHz), so SSOP etc. is out.

Many thanks in advance for your suggestions, tips and pointers for multiplexers in general.
Warren

 

SN74150 is 16-channel data selector/multiplexer.

 

True, but I'm after a 2:1 multiplexer. As I was going to sleep I realized that, for something else, I could use four 74HC245 octal bus transceivers and one 74HC139 to make an 8-bit 4:1 multiplexer. The four 1-bit active low outputs from the 74HC139 control the active low output enable lines on the 74HC245s, and all of their 8-bit outputs are tied together. Does this sound reasonable?
Thanks, Warren

 

Ok, I misunderstood what you wanted.
Use SN74HC244 octal bus driver.

 

Would a pair of 74HC257 do?

 

Thanks for the suggestions. For future readers, here are the details (i.e. I didn't know, so I'm reminding myself):

• 74HC245 is an octal tri-state bus transceiver, but it is bi-directional. So 8 bits of data can either flow left to right through the '245 or right to left, depending on the direction. An active low output enable takes the output out of high impedance.
  
• 74HC244 is also an octal tri-state bus transceiver, but it is unidirectional. 8 bits of data can only flow from left to right. An active low output enable takes the output out of high impedance.
• 74HC157 is a quad 2-to-1 multiplexer with two-state output. An active low output enable, when low, puts the input on the output. When the enable is high, the output is all low.
  
• 74HC257 is a quad 2-to-1 multiplexer with tri-state output. An active low output enable takes the output out of high impedance.

So, to multiplex two 8-bit inputs onto an 8-bit bus, you could use two 74HC257s. Or you could use two 74HC244s, but you would need a NOT gate to disable one 74HC244 output while the other is enabled.

Cheers, Warren