Urgent Decoder 4x16

[little princess]

Hi

I need to connect 2 decoders 3x8 (SN74LS138) to get a decoder 4x16 but I don't understand wich enable pin should be connected to join the IC. Could somebody help me?

Thanks

[Papabravo]

If the lines you are decoding are D, C, B, A; then connect C, B, A to the pins with that label on both of the 74LS138 chips. Connect D to G1 on one of the decoders, and on that same decoder connect G2A and G2B to logic low(GND). On the other decoder connect D to either G2A or G2B, and connnect G1 to logic high, and which ever of the G2 inputs you did not connect to D should go to logic low(GND)

Both decoders should be enabled all the time and you have a 4 x 16 decoder.

[kubeek]

Originally Posted by little princess

Hi

I need to connect 2 decoders 3x8 (SN74LS138) to get a decoder 4x16 but I don't understand wich enable pin should be connected to join the IC. Could somebody help me?

Thanks

You should connect the three input bits in parallel, and the fourth to one decoder and its negation to the other enable pin to switch the lower eight and higher eight outputs.

[BuNa]

4to16.doc

Here is an example of 4-to-16 line decoders.