Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32h7rs/STM32H7R/CEC/CEC_TXDR#0x0
CEC Tx data register
Tx data TXD is a write-only register containing the data byte to be transmitted.
https://github.com/modm-io/cmsis-svd-stm32