topic Re: LPC1778 SPI Pullups or Not? in LPCXpresso IDE

LPC1778 SPI Pullups or Not?

lpcware — Thu, 16 Jun 2016 01:39:31 GMT

Content originally posted in LPCWare by MikeSimmonds on Sun Jul 29 14:58:17 MST 2012
[FONT=Tahoma][SIZE=2]When I configure pins for SPI funtionality can I (and should I!) set the SPI_CS to have its pullup enabled?
What about the clock and data lines?

I've look at various manufacturer's datasheets for SPI devices; none seem to show pullups.

However, At least one schematic I downloaded *does* have a pullup on the CS line.

What's the best practice?

Regards, Mike :confused:

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Re: LPC1778 SPI Pullups or Not?

lpcware — Thu, 16 Jun 2016 01:39:32 GMT

Content originally posted in LPCWare by Ex-Zero on Sun Jul 29 15:30:26 MST 2012
Discussed here already: http://knowledgebase.nxp.com/showthread.php?t=2648

My favorite: CS pullup :rolleyes:

Re: LPC1778 SPI Pullups or Not?

lpcware — Thu, 16 Jun 2016 01:39:32 GMT

Content originally posted in LPCWare by MikeSimmonds on Sun Jul 29 15:38:55 MST 2012
[FONT=Tahoma][SIZE=2]Thanks for the heads up.[/SIZE][/FONT] :)

Re: LPC1778 SPI Pullups or Not?

lpcware — Thu, 16 Jun 2016 01:39:33 GMT

Content originally posted in LPCWare by MikeSimmonds on Sun Jul 29 15:49:32 MST 2012
[FONT=Tahoma][SIZE=2]However, I nearly forgot the important part of the question (which is not addressed in the thread referenced).

Can I use the on-chip pullup rather than adding an external resistor?
And at reset, the pin will be configured as an input with pullup by default.

In general, will internal pullups work or are they not enabled for outputs?

Cheers, Mike[/SIZE][/FONT][FONT=Tahoma][SIZE=2]

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Re: LPC1778 SPI Pullups or Not?

lpcware — Thu, 16 Jun 2016 01:39:33 GMT

Content originally posted in LPCWare by Ex-Zero on Sun Jul 29 17:49:19 MST 2012
As 'Fig 12 I/O configurations' of UM10470 shows, inputs use weak pullups. To avoid unintended CS activation (until your SPI setup is switching your CS to output) an external strong (10k) pullup is useful. So old-fashioned engineers add this pullup although almost all circuits work without it ;)

Re: LPC1778 SPI Pullups or Not?

lpcware — Thu, 16 Jun 2016 01:39:34 GMT

Content originally posted in LPCWare by MikeSimmonds on Mon Jul 30 01:53:52 MST 2012
[FONT=Tahoma][SIZE=2]Thanks for that

I am a firmware guy trying to talk to my hardware guy.
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