STR720 datasheet(173/401 Pages) STMICROELECTRONICS

173 / 401 page

STR720 - UART

173/401

If the mode is one where a parity bit is expected, then the bit rxfifo[x][8] (if 8 bit data + parity

mode is selected) or the bit rxfifo[x][7] (if 7 bit data + parity mode is selected) records whether

there was a parity error when that entry was received. Note, it does not contain the parity bit

that was received. ASCStatus(ParityError) is set when at least one of the valid entries in the

rxfifo has bit 8 set (if 8 bit data + parity mode is selected) or bit 7 set (if 7 bit data + parity mode

is selected).

After changing the fifoenable bit, it is important to reset the fifo to empty (by writing to the

ASCRxReset register), since the state of the fifo pointers may be garbage.

Reception is stopped by clearing the ASCControl(RxEnable) bit. A currently received frame

is completed including the generation of the receive status flags. Start bits that follow this

frame will not be recognized.

16.3.4

Timeout mechanism

The ASC contains an 8-bit timeout counter. This reloads from ASCTimeout whenever one or

more of the following is true

•

ASCRxBuffer is read

•

The ASCstarts to receive a character

•

ASCTimeout is written to

If none of these conditions hold, the counter decrements towards 0 at every baud rate tick.

ASCStatus(TimeoutNotEmpty) is ’1’ exactly whenever the rxfifo is not empty and the

timeout counter is zero.

ASCStatus(TimeoutIdle) is ‘1’ exactly whenever the rxfifo is empty and the timeout counter is

zero.

The effect of this is that whenever the rxfifo has got something in it, the timeout counter will

decrement until something happens to the rxfifo. If nothing happens, and the timeout counter

reaches zero, the ASCStatus(TimeoutNotEmpty) flag will be set.

When the software has emptied the rxfifo, the timeout counter will reset and start

decrementing. If no more characters arrive, when the counter reaches zero the

ASCStatus(TimeoutIdle) flag will be set.

STR720 数据表(PDF) 173 Page - STMicroelectronics