Common Features Description
Atmel 8051 Microcontrollers Hardware Manual 2-92
4316B–8051–02/04
RB8 in Special Function register SCON, while the stop bit is ignored. The baud rate is
programmable to either 1/32 or 1/64 the oscillator frequency.
Mode 3: 11 bits are transmitted (through TXD) or received (through RXD): a start bit (0),
8 data bits (LSB first), a programmable 9th data bit and a stop bit (1). In fact, Mode 3 is
the same as Mode 2 in all respects except the baud rate. The baud rate in Mode 3 is
variable.
In all four modes, transmission is initiated in Mode 0 by the condition RI = 0 and REN =
1. Reception is initiated in Mde 0 by the condition RI = 0 and REN = 1. Reception is initi-
ated in the other modes by the incoming start bit if REN = 1.
Serial I/O port includes the following enhancements:
• Framing error detection
• Automatic address recognition
The serial port control and status register is the Special Function Register SCON,
shown in Table 2-17. This register contains not only the mode selection bits, but also the
9th data bit for transmit and receive (TB8 and RB8), and the serial port interrupts bits (TI
and RI).
76543210
FE/SM0 SM1 SM2 REN TB8 RB8 TI RI
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