AN2354

ST10 ASC peripherals

7/21

Figure 2.

Asynchronous 9-bit data frames

1.2.2

Asynchronous transmission

the next overflow of this counter provided that SxR is set and data has been loaded into

SxTBUF. The transmitted data frame consists of three basic elements:

1.

the start bit

2.

the data field (8- or 9-bit, LSB first, including a parity bit, if selected)

3.

the delimiter (1- or 2-stop bit)

Data transmission is double-buffered. When the transmitter is idle, the transmit data loaded

into SxTBUF is immediately moved to the transmit shift register, thus freeing SxTBUF for the

next data to be sent.This is indicated by the transmit buffer interrupt request flag being set.

SxTBUF may now be loaded with the next data, while transmission of the previous one is

still going on.

The transmit interrupt request flag is set before the last bit of a frame is transmitted, that is,

before the first or the second stop bit is shifted out of the transmit shift register.

1.2.3

Asynchronous reception

A reception is initiated by a falling edge (1-to-0 transition) on pin RX, provided that bit SxR

and SxREN are set. The receive data input pin is sampled at 16 times the rate of the

selected baud rate. A majority decision of the 7th, 8th and 9th samples determines the

effective bit value. This avoids erroneous results that may be caused by noise.

Figure 3.

ASCx asynchronous mode interrupt generation

• Data bit D8

• Parity

• Wake-up bit

D2

D3

D4

D5

D7

D6

(1st)

Stop

bIt

2nd

Stop

bit

D1

D0

(LSB)

Start

bit

9th

bit