AT83SND1CXXX-ROTIL datasheet(136/212 Pages) ATMEL

136 / 212 page

136

4109J–8051–10/06

AT8xC51SND1C

17.3.3

Baud Rate Selection (Mode 0)

In mode 0, the baud rate can be either, fixed or variable.

As shown in Figure 17-6, the selection is done using M0SRC bit in BDRCON register.

Figure 17-7 gives the baud rate calculation formulas for each baud rate source.

Figure 17-6. Baud Rate Source Selection (mode 0)

Figure 17-7. Baud Rate Formulas (Mode 0)

17.4

Asynchronous Modes (Modes 1, 2 and 3)

The Serial Port has one 8-bit and 2 9-bit asynchronous modes of operation. Figure 17-8 shows

the Serial Port block diagram in such asynchronous modes.

Figure 17-8. Serial I/O Port Block Diagram (Modes 1, 2 and 3)

17.4.0.1

Mode 1

Mode 1 is a full-duplex, asynchronous mode. The data frame (see Figure 17-9) consists of 10

bits: one start, eight data bits and one stop bit. Serial data is transmitted on the TXD pin and

received on the RXD pin. When a data is received, the stop bit is read in the RB8 bit in SCON

M0SRC

BDRCON.0

PER

CLOCK

÷ 6

To Serial Port

IBRG

CLOCK

Baud_Rate=

(1-SPD)

⋅ 32 ⋅ (256 -BRL)

2SMOD1

⋅ F

PER

BRL= 256

(1-SPD)

⋅ 32 ⋅ Baud_Rate

2SMOD1

⋅ F

PER

a. Fixed Formula

b. Variable Formula

Baud_Rate

PER

TB8

SCON.3

IBRG

CLOCK

RXD

TXD

SBUF Tx SR

Rx SR

SM1

SCON.6

SM0

SCON.7

Mode Decoder

M3 M2 M1 M0

SCON.0

SCON.1

Mode & Clock

Controller

SBUF Rx

RB8

SCON.2

SM2

SCON.4

CLOCK

PER

CLOCK

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