lioryb
Posts: 8
Joined: Thu Jul 12, 2018 11:02 am

GPIO - SMI pulldown

Sun Jul 29, 2018 2:52 pm

Hi.

While trying to work with with GPIO in SMI mode (ALT2 mode), I want on of SA0-SA5 to be pulled down.
I tried to config these pins as pulled down, but they keep being pulled up (using Logic Analyzer).

Is there any restrictions on ALT2 mode to deny pulldown on GPIO-GPIO5?

Thanks

PhilE
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
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Location: Cambridge

Re: GPIO - SMI pulldown

Mon Jul 30, 2018 6:14 am

The pulls are independent of the alt functions, but they are also weak (around 50kOhm). If the pin has to be low then or should be driven low, either through the alt function (whatever it may be) or as a GPIO output.

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Burngate
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Re: GPIO - SMI pulldown

Mon Jul 30, 2018 10:18 am

As I understand it, SMI (Secondary Memory Interface) is ALT1 (ALT 2 is the DPI (VGA) interface)

GPIOs 0 - 5 are address outputs - so pulls are irrelevant?

lioryb
Posts: 8
Joined: Thu Jul 12, 2018 11:02 am

Re: GPIO - SMI pulldown

Mon Jul 30, 2018 10:56 am

Thanks both for your replies.

Burngate
Indeed, it's ALT1 not ALT2 (my typo). Yet, the pins are actually pulled up. These are so called address pins, in smi-nand driver are used as controls (NAND uses address and data multiplexed).

PhilE
I am not sure I understand your remark. in the DTS file, I changed some pins from being pulled up to be pulled down, and it had not influence on actual signal (tested with a logic analyzer connected).

Thanks

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