AT89C51ID2-SLSIM Atmel, AT89C51ID2-SLSIM Datasheet - Page 52

• Manufacturer Part Number: AT89C51ID2-SLSIM
• Description: C51ID2 64KF TWI 32KHZ PLCC44 3-5.5V IND.
• Manufacturer: Atmel

Serial I/O Port
Framing Error Detection
4289C–8051–11/05
The serial I/O port in the AT89C51ID2 is compatible with the serial I/O port in the 80C52.
It provides both synchronous and asynchronous communication modes. It operates as a
Universal Asynchronous Receiver and Transmitter (UART) in three full-duplex modes
(Modes 1, 2 and 3). Asynchronous transmission and reception can occur simultaneously
and at different baud rates
Serial I/O port includes the following enhancements:
•
•
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-
ter (See Figure 20).
Figure 20. 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 38.) 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
last data bit (See Figure 21. and Figure 22.).
Figure 21. UART Timings in Mode 1
SMOD0=X
SMOD0=1
SM0/FE
SMOD1
Framing error detection
Automatic address recognition
RXD
FE
RI
SMOD0
SM1
Start
bit
SM2
-
D0
REN
Set FE bit if stop bit is 0 (framing error) (SMOD0 = 1)
SM0 to UART mode control (SMOD0 = 0)
POF
To UART framing error control
D1
TB8
GF1
D2
RB8
GF0
D3
Data byte
D4
PD
TI
D5
IDL
RI
D6
SCON (98h)
PCON (87h)
D7
Stop
AT89C51ID2
bit
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