ST20-GP6 datasheet(82/123 Pages) STMICROELECTRONICS

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ST20-GP6

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15 UART interface (ASC)

The UART interface, also referred to as the Asynchronous Serial Controller (ASC), provides serial

communication between the ST20-GP6 and other microcontrollers, microprocessors or external

peripherals.

The ASC supports full-duplex asynchronous communication. Eight or nine bit data transfer, parity

generation, and the number of stop bits are programmable. Parity, framing, and overrun error

detection are provided to increase the reliability of data transfers. Transmission and reception of

data can simply be double-buffered, or16-deep ﬁfos may be used. For multiprocessor communica-

tions, a mechanism to distinguish the address from the data bytes is included. Testing is supported

by a loop-back option. A 16-bit baud rate generator provides the ASC with a separate serial clock

signal.

15.1 Functionality

The ASC supports full-duplex asynchronous communication, where both the transmitter and the

receiver use the same data frame format and the same baud rate. Data is transmitted on the

TXD

pin and received on the

RXD pin.

Data frames

8-bit data frames either consist of:

•

eight data bits

D0-7 (by setting the Mode bit ﬁeld to 001);

•

seven data bits

D0-6 plus an automatically generated parity bit (by setting the Mode bit ﬁeld

to 011).

Parity may be odd or even, depending on the

ParityOdd bit in the ASCControl register. An even

parity bit will be set, if the modulo-2-sum of the seven data bits is 1. An odd parity bit will be cleared

in this case.

Figure 15.1 8-bit data frames

9-bit data frames either consist of:

•

nine data bits

D0-8 (by setting the Mode bit ﬁeld to 100);

•

eight data bits

D0-7 plus an automatically generated parity bit (by setting the Mode bit ﬁeld

to 111);

•

eight data bits

D0-7 plus a wake-up bit (by setting the Mode bit ﬁeld to 101).

start

bit

8th

bit

(LSB)

1st

stop

bit

2nd

stop

bit

• Data bit (D7)

• Parity bit

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