at89c51ac3-s3sim ATMEL Corporation, at89c51ac3-s3sim Datasheet - Page 60

• Manufacturer Part Number: at89c51ac3-s3sim
• Description: At89c51ac3 Enhanced 8-bit Microcontroller With 64kb Flash Memory
• Manufacturer: ATMEL Corporation

Figure 31. Serial I/O Port Block Diagram
Figure 32. Framing Error Block Diagram
60
Framing Error Detection
Serial I/O Port
AT89C51AC3
TXD
RXD
The AT89C51AC3 I/O serial port is compatible with the I/O serial 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. To enable the
framing bit error detection feature, set SMOD0 bit in PCON register.
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 bit is set.
The software may examine the FE bit after each reception to check for data errors.
Once set, only software or a reset clears the FE bit. Subsequently received frames with
valid stop bits cannot clear the FE bit. When the FE feature is enabled, RI rises on the
stop bit instead of the last data bit (See Figure 33. and Figure 34.).
SM0/FE
SMOD
Framing error detection
Automatic address recognition
Transmitter
SMOD0
SBUF
SM1
SM2
-
Mode 0 Transmit
IB Bus
Write SBUF
SCON reg
RI
REN
Set FE bit if stop bit is 0 (framing error)
SM0 to UART mode control
POF
To UART framing error control
TI
TB8
GF1
RB8
GF0
Shift register
Receive
Receiver
SBUF
PD
TI
IDL
RI
Load SBUF
Read SBUF
Serial Port
Interrupt
Request
4383D–8051–02/08