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FantomXR

Why does the HC165 even work?

10 posts in this topic

Hey people,

I try to understand how the DIN is even working in the STM32F4-Core. 
PB14 is not going through the HCT541 buffer. It goes directly into the IC. If I understood it correctly the purpose of the HCT541 is to do a level-amplification. It takes the level from the STMs outputs (which is 3.3V - 0.4V for HIGH for CMOS or 2.4V or TTL) and amplifies them. As the HC165 and HC595 are powered from +5V they need 3.15V to see a HIGH-signal. As the HCT541 delivers 4.5V for HIGH the HC595 does of perfectly work.

But why do the HC165 even work? As I said it doesn't get an amplification. So in theory the HC165 sees 2.9V for HIGH but that's not enough so it should stay LOW and doesn't work. But it does...

Can someone explain this behavior?

Thanks,
Chris

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9 minutes ago, FantomXR said:

As I said it doesn't get an amplification

??
QH pin which is connected to the STM on SI, is an output! It sends 5V cmos level to the STM, the inputs pin of the STM are '5V tolerant' then you don't need level shifting down in this way(165 to STM).
 

Edited by Antichambre

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Oh dear... thanks for clearing my mind! ;-)

BTW: Do you watch this forum all day? ;-) 

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20 minutes ago, FantomXR said:

BTW: Do you watch this forum all day? ;-) 

lol
Yeah I've got some default pages opened when my computer is switched on, all my email boxes, messenger and midibox forum!
My computer is always switched on when I'm home. And I work 80% of the time at home so. ;)

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I have another question regarding the ICs.

For what reason do we use the HCT541? It does level-shifting and buffering. So if we want to drive only small distances, this might be obsolete? And if we take HCT595 and HCT165 the level of the signals the STM outputs should fit or not?

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Posted (edited)

DIN and DOUT modules were made a long time ago with HC, more than that with HC and 541(forJ8/9 andJ19) DIN/DOUT modules stay compatibles to all SPI ports. J8/9 J19 and J16 included.
HCT version are only 5V(Supply voltage) and J16 is a 3.3V SPI port.
But you can use HCT595/165 and remove the 541 on your own design. Keep in mind HCT need 5V supply voltage.

Edited by Antichambre

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Posted (edited)

1 hour ago, Antichambre said:

But you can use HCT595/165 and remove the 541 on your own design. Keep in mind HCT need 5V supply voltage.

Yes. But I could use LV165 or not? That could be supplied with 3V3.

Edited by FantomXR

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Posted (edited)

9 minutes ago, FantomXR said:

Yes. But I could use LV165 or not? That could be supplied with 3V3.

Yes of course, just check the levels from the datasheet.
Just take care if you use encoders, for example I never tried a pec16 with a 3V3 voltage and they are given for 5V.

Edited by Antichambre
encoder note

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Posted (edited)

The plan is not to use encoders. I'd like to use sin/con potentiometers, which will be connected to a MSP430 uC (which converts these signals to encoder-typical signals). So the whole circuit needs only 3V3. I'd like to avoid routing two supply rails on my PCB.

Edited by FantomXR

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Posted (edited)

I did some tests with this.

I connected a DIO-Board to my keyboard and the DIO-board to the core with jumper wire => no HCT541. I powered the DIO with 3V3 from the DISCO-Board. The result: It's running fine. No issues. I checked the clock with my oscilloscope. It looks very clean. Also no issues here. 

So, I think I'll leave away the HCT541 for my applications and run everything from 3V3. 

//edit: I've connected an encoder to the DIO-board. Works also fine.

Edited by FantomXR

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