AT80C51RD2 Atmel Corporation, AT80C51RD2 Datasheet - Page 34

• Manufacturer Part Number: AT80C51RD2
• Manufacturer: Atmel Corporation

Specifications of AT80C51RD2

• Max. Operating Frequency: 60 MHz
• Cpu: 8051-12C
• Max I/o Pins: 32
• Spi: 1
• Uart: 1
• Sram (kbytes): 1.25
• Operating Voltage (vcc): 2.7 to 5.5
• Timers: 4
• Watchdog: Yes

11. Serial I/O Port
11.1
Figure 11-1. Framing Error Block diagram
Figure 11-2. UART Timings in Mode 1
34
Framing Error Detection
AT80C51RD2
SMOD0=X
SMOD0=1
The serial I/O port in the AT80C51RD2 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 11-
1).
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
11-4) 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
11-2
RXD
• Framing error detection
• Automatic address recognition
FE
RI
and
Figure
SM 0/FE
SM OD1
Start
bit
1
11-3).
SM OD 0
D0
SM 1
D1
SM 2
-
D2
RE N
Se t FE bit if stop bit is 0 (fram ing erro r) (SM OD0 = 1)
SM 0 to UA RT m o de con tro l (SM OD0 = 0 )
PO F
To UA RT fra min g e rro r co nt ro l
D3
Data byte
TB8
GF1
D4
D5
RB8
GF0
D6
PD
TI
D7
IDL
RI
Stop
bit
S CO N (9 8h )
PCON (87 h)
4113D–8051–01/09
Figure
Table