SPI interface question in the LPC55S69-EVK

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SPI interface question in the LPC55S69-EVK

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NXP Employee
NXP Employee

Hi support team,

  There are three 2.2Kohm pull-up resistors connected on the LPC55S69 SPI interface in our LPC55S69 EVB. 

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Would like to ask why it needs these pull-up R for a SPI bus which has no pull-up R in general.

Are these R necessary ? Are our SPI pins(SPI_MISO, SPI_MOSI, SPI_SSEL) open-drain and must pull high externally ?  or transmission speed concern.

Thanks.

Customer: Ecolux

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NXP TechSupport
NXP TechSupport

Hi, StanleyH,

As you know that the FlexComm3 module(FC3 module) can be configured as Uart, SPI, I2C and I2S, if the FC3 is configured as I2C, it's signal pads SDA/SCL pins are Open Drain, the external pull-up resistor are required. Of course, if the FC3 is configured as SPI, the SPI signals are push-pull driven, the external pull-up resistors are unnecessary, but the 2.2K ohm pull-up resistor does take effect on the SPI data transfer.

This is the FC3 signal assignment for LPC55S69:

PIO0_2,     FC3_TXD_SCL_MISO_WS, the pin is SCL signal of I2C if FC3 is configured as I2C.

PIO0_3,      FC3_RXD_SDA_MOSI_DATA, the pin is SDA signal of I2C if FC3 is configured as I2C.

PIO0_4,     FC3_CTS_SDA_SSEL0, the pin is SDA signal of I2C if FC3 is configured as I2C.

In conclusion, all the above pads are possible to function as I2C signal, so pull-up resistor are connected in EVK in case they are I2C signals.

Hope it can help you

BR

Xiangjun Rong

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NXP Employee
NXP Employee

Hi Xiangjun,

  Understood. Thanks for the reply.

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Senior Contributor I

Hello !

I try to use SPI3 in SlaveMode and connect wires to P20 connector. One jumper is set to disable routing of SPI3 and UART0 to USB bridge. UART0 work on external connector. SPI3 not.

What can be problem ?  Logic analyze show right signals from external SPI master source but no any reaction.

Something ?

Regards,

Eugene

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