
17
TS8xCx2X2
4184I–8051–02/08
TS80C52X2 Serial I/O
Port
The serial I/O port in the TS80C52X2 is compatible with the serial I/O port in the 80C52.
It provides both synchronous and asynchronous communication modes. It operates as
an Universal Asynchronous Receiver and Transmitter (UART) in three full-duplex
modes (Modes 1, 2 and 3). Asynchronous transmission and reception can occur simul-
taneously and at different baud rates
Serial I/O port includes the following enhancements:
Framing error detection
Automatic address recognition
Framing Error Detection
Framing bit error detection is provided for the three asynchronous modes (modes 1, 2
and 3). To enable the framing bit error detection feature, set SMOD0 bit in PCON regis-
Figure 6. Framing Error Block Diagram
When this feature is enabled, the receiver checks each incoming data frame for a valid
stop bit. An invalid stop bit may result from noise on the serial lines or from simultaneous
transmission by two CPUs. If a valid stop bit is not found, the Framing Error bit (FE) in
SCON register (See
Table 9.) bit is set.
Software may examine FE bit after each reception to check for data errors. Once set,
only software or a reset can clear FE bit. Subsequently received frames with valid stop
bits cannot clear FE bit. When FE feature is enabled, RI rises on stop bit instead of the
Figure 7. UART Timings in Mode 1
RI
TI
RB8
TB8
REN
SM2
SM1
SM0/FE
IDL
PD
GF0
GF1
POF
-
SMOD0
SMOD1
To UART framing error control
SM0 to UART mode control (SMOD = 0)TS80C52X2
Set FE bit if stop bit is 0 (framing error) (SMOD0 = 1)
SCON (98h)
PCON (87h)
Data byte
RI
SMOD0=X
Stop
bit
Start
bit
RXD
D7
D6
D5
D4
D3
D2
D1
D0
FE
SMOD0=1