re help wanted in article apr csc canberra edu au u student canberra edu au ogawa taro stephen ise writes could someone please tell me if a decoder is the same as a to demultiplexer i know how to link of these to get an output circuit but how do i link of these to make a multiplexer sorry if this seems like a lame question but i m only a newbie to electronics and i have to do this circuit please make any mail as droolproof as possible thanx taro ogawa u student canberra edu au a of decoder need not be the same as a to demultiplexer although many commercial ssi implementations allow you to use one as such strictly a of decoder need only take two lines in and make one output change state according to the inputs a demux on the other hand uses two control inputs to determine which of four outputs will reflect the state of the input signal so there are three inputs required a decoder can be used as a demux if it is equipped with an output enable input since this can be used as the data input e g when high all outputs are high when low only the selected by control inputs output will be low an eight way decoder is created by using the high order bit bit to select which of two four way demuxes is enabled thus you achieve your aim of having only one output of eight reflecting the input bits note that this method cannot be used to create a true eight way demux since you have no data input the enable line on a four way decoder left once you commit the enable lines to their intended purpose a sixteen way decoder obviously requires four four way decoders plus a mechanism to enable only one of the four at a time therefore use the fifth decoder attached to the two high order bits to provide the four enable lines of course the two low order bits must be connected in parallel to the four final stage decoders please give me the credit when you submit your homework johnh electronics department school of mpce macquarie university sydney australia email johnh mpce mq edu au ph fax
