AN2354

ST10 ASC peripherals

5/21

1.1.2

Transmit and receive buffer registers

Writing to the Transmit buffer register SxTBUF (via an instruction or a PEC data transfer)

starts a transmission.

Only the number of data bit which is determined by the selected operating mode is actually

transmitted. Bits written to positions 9 through 15 of register SxTBUF are always

insignificant. After a transmission is completed, the transmit buffer register is cleared to

0000h.

Data transmission is double-buffered, so a new character may be written to the transmit

buffer register before the transmission of the previous character is complete. This allows

back-to-back transmission of characters without gaps.

Data reception is enabled by the Receiver Enable bit SxREN. After reception of a character

is completed, the received data and, if provided by the selected operating mode, the

received parity bit can be read from the (read-only) Receive Buffer register SxRBUF.

Bits in the upper half of SxRBUF which are not valid in the selected operating mode are read

as zeros.

Data reception is double-buffered, so that reception of a second character may already

begin before the previously received character is read out of the receive buffer register.

The Loop-Back option (selected by bit SxLB) allows the data currently being transmitted to

be received simultaneously in the receive buffer.

SxTBUF

Reset value: 0000h

15

14

13

12

11

10

98

765

43

210

--

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Transmit Data Buffer

--

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--

RW

SxRBUF

Reset value: 0xxxh

15

14

13

12

11

10

98

765

43

210

--

---

--

Received Data

R