Schematic question

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Schematic question

Unread postby Kabron » Thu Jul 12, 2018 5:22 pm

What is the sacral meaning of using U1, U7, U8 in the EXTERNAL IO interface?
IMHO it brings definite functional limitations due to only output directions of GPIO12, 18 and 23.
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Re: Schematic question

Unread postby crashoverride » Thu Jul 12, 2018 5:32 pm

The buffer chips (U1, 7, 8) ensure that a expansion device does not cause the ODROID-GO to malfunction. There is no loss of functionality because the pins connected can not be used as inputs.
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Re: Schematic question

Unread postby Kabron » Thu Jul 12, 2018 5:51 pm

Let me do not agree:
From the ESP32-WROVER/ESP32-WROVER-I Datasheet

IO12 14 I/O GPIO12

IO18 30 I/O GPIO18

IO23 37 I/O GPIO23
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Re: Schematic question

Unread postby Kabron » Thu Jul 12, 2018 6:09 pm

I'm considering a variant of adding JTAG pins to EXT IO by expanding the socket by 2-4 contacts
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Re: Schematic question

Unread postby crashoverride » Thu Jul 12, 2018 6:22 pm

IO12 is an ESP32 bootstrap pin. It is sampled at power on to determine the flash voltage. On WROVER, it has a pull-up resistor connected to enable 1.8V operation. If exposed without the buffer, an expansion could ground it causes 3.3V operation possibly damaging the ODROID-GO.

IO18 is the SPI-CLK. If exposed, an expansion could cause the LCD and SD card to no longer function.

IO23 is the SPI-MOSI. If exposed, an expansion could cause the LCD and SD card to no longer function.
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