Mux with memory in outputs?

Question

Hi!I have a new project and to solve  the lack of digital outputs  I amgoing to add a mux and some memory ICThe problem is that I need to control 16 outputs, lets name it from 1to 4 = A, from 5 to 9 = B and so on, but I have only 4 pins availablein my uCMy first approach is to use a mux, but I am going to control relays,so I need to hold the state for the 15 outputs that the mux is notmultiplexing.The answer is to use a simple FF-D, but I dont have a clk signal forthis porpuse, maybe a JKDo you know if something like a MUX with memory exist? or how ca Iimplement itThanks I appreciate any help

Rich Webb · Accepted Answer

A latching shift register. Conceptually, you'll have one pin as serial data in, one as clock, and one as latch. Clock in all 16 bits whenever you need to change the state of any relay and then assert the latch bit to transfer the state from the internal registers to the output drivers.

Jan Panteltje · Answer

On a sunny day (Wed, 20 Oct 2010 08:11:00 -0700 (PDT)) it happened =?ISO-8859-1?Q?Pr=E9cis_d=27electronique?= wrote in :

Why not use 2 i2c I/O expanders like PCF8574? Then you only need 2 I/O pins on the micro for 16 out.

hamilton · Answer

John Fields · Answer

---Nice one!---JF

John Fields · Answer

---Nice one!---JF

linnix · Answer

wrote ineNice chip, except for the price.   I need 3 chips per board. At 80cents each, it costs more than using a bigger micro.  HC595 at 30cents each is more cost effective.

Jan Panteltje · Answer

On a sunny day (Wed, 20 Oct 2010 12:06:14 -0700 (PDT)) it happened linnix wrote in :

Yes it is expensive, but you can use pins at input too. To be honest, after posting that I though: Replace it all with a PIC. I mean the PIC, if a 20 pins, can do 16 I/O, use the internal osc, 2 power pins, and 2 i2c, so one chip at maybe 2 $ or 3 $. And perhaps it can replace the original processor too :-)

linnix · Answer

amabl=3Dr pins,Actually, this even better for me.  I can use 2 chips for 18 ports and it got open-drain (no worry about shorting outputs).  But using Maxim chip scaresme.

Nico Coesel · Answer

Did you look into the Cortex M0 devices from NXP (LPC1100 series)?AFAIK they are pretty cheap.-- Failure does not prove something is impossible, failure simplyindicates you are not using the right tools...nico@nctdevpuntnl (punt=.)--------------------------------------------------------------

linnix · Answer

:nixte:Rev 1 is a $5 micro.-This is rev 2, $3 micro + $2 I/OYes, they are rev 3, $3 micro + $1 (micro I/O)Rev 4 is $3 micro + 50 cents I/O.

Mux with memory in outputs?

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