AT89C51ED2 Atmel Corporation, AT89C51ED2 Datasheet - Page 48

• Manufacturer Part Number: AT89C51ED2
• Manufacturer: Atmel Corporation

Specifications of AT89C51ED2

• Flash (kbytes): 64 Kbytes
• Max. Operating Frequency: 60 MHz
• Cpu: 8051-12C
• Max I/o Pins: 32
• Spi: 1
• Uart: 1
• Sram (kbytes): 2
• Eeprom (bytes): 2048
• Self Program Memory: API
• Operating Voltage (vcc): 2.7 to 5.5
• Timers: 4
• Isp: UART
• Watchdog: Yes

14. Serial I/O Port
14.1
48
Framing Error Detection
AT89C51RD2/ED2
The serial I/O port in the AT89C51RD2/ED2 is compatible with the serial I/O port in the 80C52.
It provides both synchronous and asynchronous communication modes. It operates as a Univer-
sal 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 register (See Figure 14-
1).
Figure 14-1. 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
14-4.) bit is set.
Software may examine FE bit after each reception to check for data errors. Once set, only soft-
ware 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
14-2. and Figure 14-3.).
Figure 14-2. UART Timings in Mode 1
• Framing error detection
• Automatic address recognition
SMOD0=X
SMOD0=1
SM0/FE
SMOD1
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
bit
4235K–8051–05/08