Pull-up/down resistors for UART

[alexeypanteleyc]

Hello!

Could you please advise if it's correct to connect MK10 to MKM33 without external pull-up or pull-down resistors?

Please find attached the block diagram.

Here we connect main MCU MK10DX256VLK7 to the metering MCU MKM33Z128ACLH5 and set UART0_TX pin for output, and PTI0 pin for input with internal pull-up/down.

When data goes from MKM33Z128ACLH5  to MK10DX256VLK7  we set PTI0 as output, and UART0_RX as input with internal pull-up/down.

Resistors R50 and R53 are used for nanosecond noise elimination. Vcc is is 3.3V.

Could you please advise if this implementation is correct or we need to add external pull-up/down resistors?

Thanks and regards,

Alexey

[MarMi · Accepted solution]

Dear Alexey,

PTI1 (SCI1_TxD on pin #56) of the MKM33Z128ACLH5 is designed as open drain to achieve 5V tolerance. It requires an external pull-up resistor for correct operation. As an external pull-up resistor, you can use an internal pull-up of the MK10DX256VLK7, that could be set on UART0_RxD (pin #35) operating in input mode. However, the weak internal pull-up of the MK10DX256VLK7 device might be limiting maximum communication data rate and therefore for achieving faster data rates and/or improving immunity of the communication line to external noises, you might still consider adding an external pull-up.

Kind regards,

Martin M.