2. Read-Modify-Write to SCON (SETB, CLR, CPL, ANL, ORL, XRL, JBC)
Read-Modify-Write (RMW) instructions may cause a loss of
UART interrupt information if used with any bit in SCON,
i.e. the RMW instructions need to be treated as a direct move
to SCON such as MOV SCON,#IMM. These instructions may be used
when it is not possible for the interrupt to occur at the same
time as the instruction is being executed, which means in
the following circumstances:
A. The UART is not currently operating, or
B. Within a short period of time after TI or RI is set during
half-duplex communications, or
C. Within a short period of time after both TI and RI are set
during full-duplex communications, and before the next byte
is transmitted.