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General SPI Questions - 74HCxxx digital isolator

SPI

Best Answer NooM , 23 November 2013 - 03:38 PM

your pins look correct.

miso is in.

 

a thing to note: it actually doesent matter on what the chip starts, the netduino pulls the pins low/high when its configured, meanwhile they are normally floating on any other device.

id take the high version tho.

 

thats not netduino releated, but on my avr's i have to pull the chipselect of the devices high manually, or they will interrupt my isp programmer (wich also uses spi port) - cos on floating state the spi devices think the data is for them. (low normally means "enable" for a spi device)

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#1 stotech

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Posted 22 November 2013 - 07:50 AM

I want to use a digital isolator with a circuit that closely resembles the magical bit shift shizzle here.

 

The part I've chosen is this.

 

Which resembles the top image here.

 

5 output channels and 1 input channel. I hoped to wire it like below. Any objections. My only worry was that my basic understanding of SPI was out and that the in latch might actually go the other way than I noted here. But I don't think so? I think this is right? Can someone confirm that I've got the direction of all the pins right?

 

SPI Clk     ----->

 

Miso         <-----

 

Mosi         ----->

 

In Latch    ----->     ???

 

Out Latch ----->

 

OE           ----->

 

Sorry about the links. The My Media TAB has never worked on my account?

 

Grant


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#2 stotech

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Posted 22 November 2013 - 10:44 AM

The chip comes with the option of starting hi or low when there is no power at the input. Any suggestions on the effect this might have on the SPI interface. I remember hearing something about it needing to be idle low so i'm leaning toward the [font="arial, helvetica, sans-serif;font-size:small;"]SI8661BC-B-IS1 as opposed to the [/font][font="arial, helvetica, sans-serif;font-size:small;"]SI8661EC-B-IS1 which defaults to high on no signal.[/font]

 

[font="arial, helvetica, sans-serif;font-size:small;"]Thanks in advance.[/font]



#3 NooM

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Posted 23 November 2013 - 03:38 PM   Best Answer

your pins look correct.

miso is in.

 

a thing to note: it actually doesent matter on what the chip starts, the netduino pulls the pins low/high when its configured, meanwhile they are normally floating on any other device.

id take the high version tho.

 

thats not netduino releated, but on my avr's i have to pull the chipselect of the devices high manually, or they will interrupt my isp programmer (wich also uses spi port) - cos on floating state the spi devices think the data is for them. (low normally means "enable" for a spi device)



#4 stotech

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Posted 23 November 2013 - 10:26 PM

Thanks for the advice. That's exactly the type of response I wanted. I always assume that there is something I've over looked like that. Thanks for going the extra mile.







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