TheUART in the 8XC5X operates identically to the
UART in the 80C51 except for the following enhsncementa.
For a complete understanding of the 8XC5X
UART please refer to the description in the 30C51
Hardware Description chapter in the Embedded Microcontroller’sand
ProcessorsHandbook.
Franting Error Detection-Framin g Error Detection
allows the serial port to check for valid stop bits in
modes 1, 2 or 3. A missing stop bit can be caused for
example, by noise on the seriallinesj or transmission by
two CPUS simultaneously.
If a stop bit is missing a Framing Error bit (FE) is set.
The FE bit can be checkedin softwsre after each reception
to detect communication errors. Once set, the FE
bit must be cleared in sotlwsre. A valid stop bit will not
clear FE.
The FE bit is located in SCON and shares the same bit
addreesas SMO.Control bit SMODOin the PCON register
(location PCON.6) determines whether the SMO
or FE bit is amessed. If SMODO= O,then mcesaes to
SCON.7 are to SMO.If SMODO= 1, then -ses to
SCON.7 are to FE.
Automatic Address R eeognition-Autornatic Address
Recognition reduces the CPU time required to service
theserialport.SincetheCPUisonlyinterruptedwhen
it receives its own address, the software overhead to
compare addresses is eliminated. With this featureenabled
in one of the 9-bit modes, the Receive Interrupt
(RI) tlag will only get set when the received byte corresponds
to either a Oiven or Broadcast address.