Product Specs

Table Of Contents
35 UARTE Universal asynchronous receiver/
transmitter with EasyDMA
Page
334
TXDRDY
TXDRDY
TXDRDY
TXDRDY
TXDRDY
0
1
2
N-2
N-1
N
The .PTR and .MAXCNT registers are double-buffered. They can be updated and prepared for the next RX/
TX transmission immediately after having received the RXSTARTED/TXSTARTED event.
The ENDRX/ENDTX event indicates that EasyDMA has finished accessing respectively the RX/TX buffer in
RAM.
35.3 Transmission
The first step of a DMA transmission is storing bytes in the transmit buffer and configuring EasyDMA. This
is achieved by writing the initial address pointer to TXD.PTR, and the number of bytes in the RAM buffer to
TXD.MAXCNT. The UARTE transmission is started by triggering the STARTTX task.
After each byte has been sent over the TXD line, a TXDRDY event will be generated.
When all bytes in the TXD buffer, as specified in the TXD.MAXCNT register, have been transmitted, the
UARTE transmission will end automatically and an ENDTX event will be generated.
A UARTE transmission sequence is stopped by triggering the STOPTX task, a TXSTOPPED event will be
generated when the UARTE transmitter has stopped.
If the ENDTX event has not already been generated when the UARTE transmitter has come to a stop, the
UARTE will generate the ENDTX event explicitly even though all bytes in the TXD buffer, as specified in the
TXD.MAXCNT register, have not been transmitted.
If flow control is enabled, a transmission will be automatically suspended when CTS is deactivated and
resumed when CTS is activated again, as illustrated in Figure 94: UARTE transmission on page 334.
A byte that is in transmission when CTS is deactivated will be fully transmitted before the transmission is
suspended.
2
Figure 94: UARTE transmission
The UARTE transmitter will be in its lowest activity level, and consume the least amount of energy, when
it is stopped, i.e. before it is started via STARTTX or after it has been stopped via STOPTX and the
TXSTOPPED event has been generated. See POWER Power supply on page 78 for more information
about power modes.
35.4 Reception
The UARTE receiver is started by triggering the STARTRX task. The UARTE receiver is using EasyDMA to
store incoming data in an RX buffer in RAM.
1
Lifeline
CTS
TXD
TXD.MAXCNT = N+1
STARTTX
TXSTARTED
ENDTX
TXDRDY