SPI pull up/down rezistors

[lpcware]

Content originally posted in LPCWare by Forrest on Tue Nov 29 02:08:20 MST 2011
Hi all,

I would like to ask any engineer how pins are configured if I set it to spi mode.
Is it open-drain or any other type? So engineer from my company suggest my
add pull-up rezistors to all spi pins. But I think its not important.
This design is for industry so it must be robust.

Thanks Forrest

[lpcware]

Content originally posted in LPCWare by Polux rsv on Tue Nov 29 10:15:28 MST 2011

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Quote: Zero
Hardware engineers are always anxious :eek:, so just add 10k...

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Because software engineers can't imagine the effects of missing resistors in terms of cost and delay of a such simple correction :D

Angelo, hardware engineer :rolleyes:

[lpcware]

Content originally posted in LPCWare by NXP_Europe on Tue Nov 29 05:20:44 MST 2011

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Quote: forrest
Hi all,

I would like to ask any engineer how pins are configured if I set it to spi mode.
Is it open-drain or any other type? So engineer from my company suggest my
add pull-up rezistors to all spi pins. But I think its not important.
This design is for industry so it must be robust.

Thanks Forrest

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It is good practice to add pull-up/pull-down resistors in such cases, especially the control lines to avoid any confusion in their default states.

[lpcware]

Content originally posted in LPCWare by Ex-Zero on Tue Nov 29 04:00:27 MST 2011

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Quote:

...engineer from my company suggest my add pull-up rezistors...

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Hardware engineers are always anxious :eek:, so just add 10k...

[lpcware]

Content originally posted in LPCWare by Polux rsv on Tue Nov 29 02:26:24 MST 2011
At least insert a pull-up on the CS line. This is to avoid peripheral beeing selected during reset phase, where ios are not configured yet.

A good practice is to add resistors on every line you have a doubt. After testing, if the resistor is not really needed, you simply remove it on the pcb assembly by removing the resistor from the bom. No raw pcb changes, no ICT tools modification, no blablabla, very small expenses.
But if you don't put it on your schematics, and the resistor is needed, you will have to modify your prototypes, redesign the pcb, modify production tooling, .....which is more expensive, will delay your "start production date".

Angelo

[lpcware]

Content originally posted in LPCWare by Rob65 on Tue Nov 29 02:23:11 MST 2011
If it needs to be robust then you [B]always[/B] add resistors, even if the microcontroller states it is not needed.

If these need to be pull up or down resistors depends on your device (e.g. is the SPI clock high or low when not active)

Rob