The configured LIN-UART baud rate 1.2 kps is not accurate when peripheral clock is 40 MHz. Why and how to get the expected baud rate?
The LIN-UART baud rate is generated from a 15-bit reload counter, by setting a value to baud rate generator register (BGR). For a baud rate of 1.2 kps, the reload value for BGR is 0x8234 ((40*10^6/1200)-1), which violates the maximum value of a 15-bit counter 0x7FFF. To get the expected baud rate, select the available clock frequency and BGR value as listed in Table 1.
Table 1. Baud Rate Setting Example for Each Internal Clock Frequency
For more information on LIN-UART baud rate, see MB91590 Series FR81S Hardware Manual