Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Freescale Semiconductor/MK61F15WS/UART1/ET7816#0x0
TXTHRESHOLD=0
UART 7816 Error Threshold Register
Receive NACK Threshold
Transmit NACK Threshold
0 (0): TXT asserts on the first NACK that is received.
1 (1): TXT asserts on the second NACK that is received.
https://github.com/cmsis-svd/cmsis-svd-data