Project Discussion Assistance

Thought for 54 sec

For U1, the datasheet confirms the required logic states at reset for these strapping pins, but it does not give a specific external resistor value. A standard, safe recommendation is 10 kOhm external pulls.

Recommended wiring for U1 strapping pins

Table

Pin on U1	Required reset state from datasheet	Recommended resistor	Wiring
`GPIO12 / MTDI`	Low at power-up	10 kOhm Generic Resistor	`GPIO12` -> resistor -> `GND`
`GPIO5`	Default state is pull-up / 1	10 kOhm Generic Resistor	`GPIO5` -> resistor -> `3V3`
`GPIO15 / MTDO`	Default state is pull-up / 1	10 kOhm Generic Resistor	`GPIO15` -> resistor -> `3V3`

Datasheet basis

Table

Pin	Datasheet statement
`GPIO12 / MTDI`	Must be kept low during power-up; `MTDI=0` keeps `VDD_SDIO` at 3.3 V
`GPIO5`	Strapping pin with internal weak pull-up
`GPIO15 / MTDO`	Strapping pin with internal weak pull-up

Why 10 kOhm

The datasheet says strap states can be overridden with external pull-up/pull-down resistances.
Internal pulls are typically 45 kOhm.
10 kOhm is a common strong-enough external value to dominate the internal weak pull and improve noise immunity.

Exact net intent

Table

New resistor function	Connect between
Pull-down for `GPIO12`	U1 `GPIO12` and `GND`
Pull-up for `GPIO5`	U1 `GPIO5` and `3V3`
Pull-up for `GPIO15`	U1 `GPIO15` and `3V3`

If you want, I can next give you the matching fix for U6 as a short wiring checklist too.

CCS811 wiring checklist

Check missing pull resistors

Add resistor designators

J1 SHIELD__3 - J2 P2

U1 EN - R5 P2

U3 VOUT - U1 VDD

U1 IO34 - J3 1

U1 SENSOR_VP - U5 A1

U1 SENSOR_VN - J3 2

Reviews

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