Enhanced Serial Communication Interface (eSCI)
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor 31-29
31.4.5.2.2 Frame and Character Transmission
The transmitter starts the transmission of a data frame or special character when the condition for the start
transition as described in Table 31-24 is fulfilled. There are three source for data or character transmission.
The priority among these source are specified in Table 31-25. All three sources can be available at one
point in time.
31.4.5.2.3 CPU Controlled SCI Data Frame Transmission
The transmission of a data frame is started when the transmitter is in its ready state and only the commit
bit iCMT is set.
As the first step, the content of the eSCI SCI Data Register (eSCI_SDR) is transferred into the internal
transmitter shift register. When this transfer is finished, the internal commit bit iCMT is cleared and the
transmit data register empty flag TDRE in the eSCI Interrupt Flag and Status Register 1 (eSCI_IFSR1) is
set. If the transmit interrupt enable bit TIE in the eSCI Control Register 1 (eSCI_CR1) is also set, the
TDRE flag generates a transmitter interrupt request.
The transmitter shift register then shifts a frame out through the TXD output signal, which is prefaced with
a start bit and appended with the parity bit, if configured, and the configured number of stop bits.
When the last stop bit has been transmitted and the application has not disabled the transmitter, the
transmitter returns to the ready state via the done transition. If no frame or character transmit request is
pending, the transfer complete flag TC in the eSCI Interrupt Flag and Status Register 1 (eSCI_IFSR1) is
set.
If the application has disabled the transmitter while the frame is transmitted and stop bit has been
transmitted, the transmitter goes into the idle state via the halt transition. The transfer complete flag TC in
Table 31-24. Transmitter Module Transitions
Transition Condition Action Description
start (State = Ready)
and
(SBK=1 or iPRE=1 or iCMT=1)
TACT = 1 Start of transmission of data frame or special character
when data are available or character transmission
request is pending.
done State = Run
and
last stop bit transmitted
TACT = 0
TC =
(SBK & iPRE & TC)
Finished transmission of data frame or special
character and transmitter still enabled. Transmission is
complete if no transmit request is pending.
halt State = Stop
and
last stop bit transmitted
TACT = 0
TC = 1
iCMT = 0
Finished transmission of data frame or special
character and transmitter was disabled.
Table 31-25. Transmit Source Priority
Priority Indication Transmission Source
(highest) 0 eSCI_CR1[SBK] = 1 Break character.
1 iPRE = 1 Preamble.
(lowest) 2 iCMT = 1 eSCI SCI Data Register (eSCI_SDR) frame.
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