AT80SND1C-ROTIL datasheet(134/210 Pages) ATMEL

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134

AT8xC51SND1C

4109E–8051–06/03

Serial I/O Port

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

nous communication 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 auto-

matic address recognition.

Mode Selection

SM0 and SM1 bits in SCON register (see Figure 125) are used to select a mode among

the single synchronous and the three asynchronous modes according to Table 123.

Table 123. Serial I/O Port Mode Selection

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

purposes 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.

Timer 1

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

in Figure 94 Timer 1 is used in its 8-bit auto-reload mode (detailed in Section "Mode 2

(8-bit Timer with Auto-Reload)", page 53). SMOD1 bit in PCON register allows doubling

of the generated baud rate.

Figure 94. Timer 1 Baud Rate Generator Block Diagram

SM0

SM1

Mode

Description

Baud Rate

Synchronous Shift Register

Fixed/Variable

8-bit UART

Variable

9-bit UART

Fixed

9-bit UART

Variable

TR1

TCON.6

GATE1

TMOD.7

Overflow

C/T1#

TMOD.6

TL1

(8 bits)

TH1

(8 bits)

INT1

PER

CLOCK

÷ 6

SMOD1

PCON.7

÷ 2

CLOCK

To serial

Port

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