SN54LS138: SN54LS138

krishnaprasad MB

Part Number: SN54LS138
Other Parts Discussed in Thread: TMS320F28388D, SN74LV138AT

Hi,

I am using the line decoder SN54LS138 for creating multiple chip select signals for interfacing with external asynchronous memory devices like ADC, DAC , RDC etc. I used the address pins A0,A1 from my processor TMS320F28388D to be interfaced with decoder, where the A2 pin of SN54LS138 has connected to GND. Since the A2 address pin of processor has already been allocated to other multiplexed operations, I cant use that pin for address line options.

Is it recommended to ground the A2 pin of line decoder while the other two pins viz. A0 and A1 been connected to processor address lines?

I have referred may reference designs of the same, but nowhere is being mentioned.

over 1 year ago

0 Clemens Ladisch over 1 year ago

Guru 290550 points

You must not let any input float.

If you use only two Ax inputs, then you can get only four outputs. If A2 is low, you get the first four outputs; if A2 is high, you get the last four outputs.

(Why did you choose a military-grade bipolar device? The SN74LV138AT is cheaper and uses less power.)

0 krishnaprasad MB over 1 year ago in reply to Clemens Ladisch

Prodigy 60 points

Thanks for your prompt response on the subject matter.

We are working for a defense application. That's why we required to opt for mil-grade components.

Actually, for our requirement, we need only four outputs(Y0,Y1,Y2 and Y3).So in that case, can we make A2 pin of SN54ls138 permanently ground instead of connecting it to processor ?

0 Clemens Ladisch over 1 year ago in reply to krishnaprasad MB

Guru 290550 points

Yes.

0 krishnaprasad MB over 1 year ago in reply to Clemens Ladisch

Prodigy 60 points

Thanks

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SN54LS138: SN54LS138