Is it possible to use UART1 and external memory
When P4.0 & P4.1 are set up as UART1 pins, it is only possible to receive data when P2.3 is high.
P2.3 can be configured as an output or an input, but its level must be high.
Another workaround is to use P2.3 as SIN1 function instead of P4.0. P4.1 can remain as SOUT1
P4.0 can be used as a GPIO (with P4.0 high or low and set up as input or output - full flexibility allowed on P4.0 as a GPIO).
Unfortunately, this workaround is not good if P2.3 is intended to be used as a GPIO or external memory AE function.