AT83SND1CXXX-ROTIL datasheet(133/212 Pages) ATMEL

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133

4109J–8051–10/06

AT8xC51SND1C

17. Serial I/O Port

The serial I/O port in the AT8xC51SND1C provides both synchronous and asynchronous com-

munication modes. It operates as a Synchronous Receiver and Transmitter in one single mode

(Mode 0) and operates as an Universal Asynchronous Receiver and Transmitter (UART) in three

full-duplex modes (Modes 1, 2 and 3). Asynchronous modes support framing error detection and

multiprocessor communication with automatic address recognition.

17.1

Mode Selection

SM0 and SM1 bits in SCON register (see Figure 115) are used to select a mode among the sin-

gle synchronous and the three asynchronous modes according to Table 113.

Table 113. Serial I/O Port Mode Selection

17.2

Baud Rate Generator

Depending on the mode and the source selection, the baud rate can be generated from either

the Timer 1 or the Internal Baud Rate Generator. The Timer 1 can be used in Modes 1 and 3

while the Internal Baud Rate Generator can be used in Modes 0, 1

and 3.

The addition of the Internal Baud Rate Generator allows freeing of the Timer 1 for other pur-

poses in the application. It is highly recommended to use the Internal Baud Rate Generator as it

allows higher and more accurate baud rates than Timer 1.

Baud rate formulas depend on the modes selected and are given in the following mode sections.

17.2.1

Timer 1

When using Timer 1, the Baud Rate is derived from the overflow of the timer. As shown in

Figure 17-1 Timer 1 is used in its 8-bit auto-reload mode (detailed in Section "Mode 2 (8-bit

Timer with Auto-Reload)", page 54). SMOD1 bit in PCON register allows doubling of the gener-

ated baud rate.

SM0

SM1

Mode

Description

Baud Rate

Synchronous Shift Register

Fixed/Variable

8-bit UART

Variable

9-bit UART

Fixed

9-bit UART

Variable

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