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Forum Index : Microcontroller and PC projects : Quick SPI CS question....

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Grogster

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Joined: 31/12/2012
Location: New Zealand
Posts: 9753
Posted: 05:06am 30 Oct 2018
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SPI LCD panel with touch. If I KNOW I won't ever want the touch feature, and that the LCD will always be used, can I tie LCD_CS and TOUCH_CS pins on the LCD high, and NOT use pins for them on the MM?

I am hoping to reclaim two pins in the next PCB version, by doing that.
Does that sound like sane logic?

EDIT: .....and also claim back the pin for the touch IRQ, which also won't be used....Edited by Grogster 2018-10-31
Smoke makes things work. When the smoke gets out, it stops!
 
erbp
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Joined: 03/05/2016
Location: Australia
Posts: 195
Posted: 07:41am 30 Oct 2018
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You would need to tie the LCD_CS pin on the LCD to GROUND, so that the display controller will be permanently enabled.

You need to tie the TOUCH_CS pin on the LCD to 3v3, so that the touch controller is permanently disabled.

This assumes you do not use the SPI channel to communicate with any other SPI device(s), if you did you would need to leave the LCD_CS pin connected to the MM and include it in the OPTION LCDPANEL configuration settings, as the display controller would need to remain software selectable so as not to interfere with the other SPI device.

Cheers,
Phil.
 
Grogster

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Joined: 31/12/2012
Location: New Zealand
Posts: 9753
Posted: 07:44am 30 Oct 2018
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Lovely, thanks.

Yes, the only thing on the SPI bus, is the LCD - and the touch controller I don't want to use.

I will ground LCD_CS, and tie high TOUCH_CS. That should do it, yes?
Smoke makes things work. When the smoke gets out, it stops!
 
matherp
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Joined: 11/12/2012
Location: United Kingdom
Posts: 10572
Posted: 08:13am 30 Oct 2018
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You need to be a bit careful, some SPI devices only work if the CS line is active. Suggest you test with the specific display before going to copper
 
Grogster

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Joined: 31/12/2012
Location: New Zealand
Posts: 9753
Posted: 08:22am 30 Oct 2018
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Good advise, thanks. I will.
Smoke makes things work. When the smoke gets out, it stops!
 
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