Interview question

[Nagarathna]

Hi,

I had been to an interview last weekend and was asked a question.

Interviewer : i have 8 gpio pins in a controller and i want to controll and access 16 devices how would u do it ?


Me : I wouls use a mux

but the interviewer was not satisfied with the answer hence plz do suggest me with
other options and ideas if any.

Thanku

 

[wannaBinventor]

That's what I would do, but then again I have a business degree and as such won't be interviewing for any engineering jobs any time soon. In other words, I can't say. However, since he said "control and access" I would have said that you need a mux and demux.

Maybe he just wanted you to elaborate or engage him further on what kind of devices you would be controlling, communication protocol, etc.

 

[skyhawk]

If the devices were LEDs, perhaps charlieplex.

Charlieplexing - Wikipedia, the free encyclopedia

 

[AtomSoft]

I would have asked him ... would i be required to read data back to the MCU ? if so a port expander... else multiplexing...

 

[cc1984]

When I read your interview question, I thought the same as you (use a mux). Thinking further, I think I would have had to ask several questions:
1. What is the control signal? On/Off, serial, binary.....
2. Can the devices be programmed to accept an address (identifier)?- with eight IO pins you should be able to address....255 devices.


These questions would have to be answered for me to start answering the question....

Did you get the job?

 

[Mike - K8LH]

Pick one;

(1) I would be happy to provide you with a quote if you can provide fully qualified specifications.
(2) If you don't have specifications I could help you write the specifications at a reasonable T&M rate.
(3) Damn it Jim, I'm a Doctor, not an Engineer.

and, how about,

(4) If you'd like, I can probably show you how to do it with 6 GPIO pins (LOL)...

 

[Gayan Soyza]

They are judging whether you have experienced in Input Output expanding.

Also they checking whether you have component knowledge rather than common names like multiplexers,decoders etc.......

I think we need judges like that.

 

[Mosaic]

Pick one;

(4) If you'd like, I can probably show you how to do it with 6 GPIO pins (LOL)...

Ok...4 x 4 pins gives u a 16 way mux. 3 x 3 a 9 way......or less if u use serial with 74hc595 parallel latches.

How does 6 do 16?