STV3550 datasheet(117/144 Pages) STMICROELECTRONICS

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STV3550

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of a second character is complete. The previously received character in the receive buffer is

overwritten, and the ASC_n_Status register is updated to reflect the reception of the new character.

The loop-back option (selected by the LoopBack bit) internally connects the output of the

transmitter shift register to the input of the receiver shift register. This may be used to test serial

communication routines at an early stage without having to provide an external network.

7.8.2

Data Frames

Data frames may be 8-bit or 9-bit, with or without parity and with or without a wake-up bit. The data

frame type is selected by the setting of the Mode bit field in the control register.

The transmitted data frame consists of three basic elements:

●

The start bit

●

The data field (8 or 9 bits, least significant bit (LSB) first, including a parity bit or wake-up bit, if

selected)

●

The stop bits (0.5, 1, 1.5 or 2 stop bits)

7.8.2.1 8-bit Data Frames

Figure 71 illustrates a 8-bit transmitted data frame. 8-bit frames may use of one of the following

formats:

●

Eight data bits D0-7 (Mode set to 001)

●

Seven data bits D0-6 plus an automatically generated parity bit (Mode set to 011)

Parity may be odd or even, depending on the ParityOdd bit in the ASC_n_Control register. If the

modulo 2 sum of the seven data bits is 1, then the even parity bit will be set and the odd parity bit will

be cleared.

In receive mode the parity error flag (ParityError) will be set if a wrong parity bit is received. The

parity error flag is stored in the 8th bit (D7) of the ASC_n_RxBuffer register.The parity error bit is

set high if there is a parity error.

7.8.2.2 9-bit Data Frames

Figure 72 illustrates a 9-bit transmitted data frame. 9-bit data frames use of one of the following

formats:

●

Nine data bits D0-8 (Mode set to 100)

●

Eight data bits D0-7 plus an automatically generated parity bit (Mode set to 111)

●

Eight data bits D0-7 plus a wake-up bit (Mode set to 101)

Figure 71: 8-bit Tx Data Frame Format

start

bit

8th

bit

(LSB)

1st

stop

bit

2nd

stop

bit

• Data bit (D7)

• Parity bit

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