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MKE04  UART0 TX on PTA3 pullup

Question asked by Jaroslav Brazdil on Aug 19, 2016
Latest reply on Sep 4, 2016 by Jaroslav Brazdil


I used Uart0 Tx signal on PTA3 pin on my design with MKE04Z8VFK4.

The first set of 15 pcs of the module works fine.

I have new set of 25pcs of same module, no one of them works.


The problem is with UART0 Tx signal. PTA3 pin is open drain, so I use Internal pullup resistor by PORT_PUEL register.

It works fine for the first 15pcs , the Tx signal (connected directly to SN65HVD485 driver) is clear, more then 4V high.

It does not  work for new set of modules. System ROM and SIM_SRSID is same for all MCUs.


So the question is, how the pullups works, is it possible tu use pullups for UART?

If not, why one set of MCU works (all of them, with Tx level over 4V) and another set not (no one works)?

System ROM and SIM_SRSID is same for all MCUs.


When I set the pullup, the Tx signal goes high (4,5V), when I enable the transmitter (set UART0_C2    TE)

the Tx signal drops to 0.


I can use external pullup, but I have 40 modules ready and external resistor is not exactly elegant.