Is there a chip for this?

[RickAlty]

This schematic... http://members.aol.com/rick7card/flipflop.jpg

should, if I have my basic theory right, double the number of available outs by sending inputs 1-6 to either outputs 1a-6a or 1b-6b depending on whether input 7 is high or low. While it's easy enough with transistors, it struck me that it might well be the sort of thing there's already a CMOS chip to do. Anyone know how to search for such a thing?

Richard

 

[andrewpro]

Unless I'm misunderstanding the schematic, it's jsut an A/B switch so to speak. Youll either switch all 6 inputes to the even or odd output pins. There is also no latchingg capability, so if you change anyhting on "channel A" then switch to "channel B" the same thing will be on channel B and channel A will be, in essene, disconnected.

This will increase the number of things you can do at one time with the outputs, but wont increase the number of available I/O youve got. Basically, it's "pins 1-6 do either this or this" not this AND this.

You could use a latching shift register and jsut two pins to actually increase the outputs you could have. If your using an X part, you could use various I2C I/O chips. They're a bit more difficult to use, but give bi-directional programable I/O. Take a look at the Maxim MAX7300 or Microchip MCP23016. These use enough command and control bytes to be compatible with the picaxes I2C i/o and can give you up to 160+ I/O's off just two pins.

 

[RickAlty]

Hi, Andy, yes, just a simple A/B with no latching is what I want. The output will be going to a latching LED driver. Once it's gotten its signal, it sets the display and leaves it there. If I want to change the readout on, say, LED bank 9, I set the high/low pin to high, and send the clock pulse out on input 3.

Richard

 

[andrewpro]

Ahh..ok. In that case your looking for a multiplexer (AKA Data Selector). There is a chip called a 74xx157 (xx's are for family, like a 74LS157 or 74HC157) that is a quad 2 to 1 multiplexer. You can connect it backwards too, so i'ts a 1 to 2. There are 4 2 to 1's on each chip, so youd need two to makee the 6 inputs, but can just ignore the last two (of the 8 available). Wire it up resembling the concept in your origional post, and youll be good to go. I dont know if there is a hex or octal version (6 or 8), but it might be worth looking into if your worried about chip count.

Edited by - andypro on 4/12/2005 12:46:18 AM

 

[RickAlty]

Thanks, Andy, that would do it. I did have a look through google for a hex or oct version, but couldn't find one. Two of the quads will be fine though, they're only a quarter a pop.