RM0319 datasheet(224/368 Pages) STMICROELECTRONICS

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Asynchronous serial ports (UART)

RM0319

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Doc ID 022640 Rev 3

The nUARTRTS signal is reasserted when data has been read out of the receive FIFO so

that it is filled to less than the watermark level. If RTS flow control is disabled and the UART

is still enabled, then data is received until the receive FIFO is full, or no more data is

transmitted to it.

CTS flow control

If CTS flow control is enabled, the transmitter checks the nUARTCTS signal before

transmitting the next byte. If the nUARTCTS signal is asserted, the byte is transmitted,

otherwise transmission does not occur. Data continues to be transmitted while nUARTCTS

is asserted and the transmit FIFO is not empty. If the transmit FIFO is empty and the

nUARTCTS signal is asserted, no data is transmitted.

If the nUARTCTS signal is deasserted and CTS flow control is enabled, the current

character transmission is completed before stopping. If CTS flow control is disabled and the

UART is enabled, the data continues to be transmitted until the transmit FIFO is empty.

16.5.2

Modem operation

This section describes the modem operation for UART0 and UART1.

UART0 and UART1 (expanded automation and small printer modes) are allowed to support

both data terminal equipment (DTE) and data communication equipment (DCE) modes of

operation. Table 65 shows the meaning of DTE and DCE signals.

Table 65.

Meaning of UART0/1 modem input/output in DTE and DCE modes

Signal

Meaning

DTE

DCE

nUARTCTS

Clear to send

Request to send

nUARTDSR

Data set ready

Data terminal ready

nUARTDCD

Data carrier detect

nUARTRI

Ring indicator

nUARTRTS

Request to send

Clear to send

nUARTDTR

Data terminal ready

Data set ready

nUARTOUT1

Data carrier detect

nUARTOUT2

Ring indicator

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