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Chapter 38 Universal Asynchronous Receiver/Transmitter(UART)
At this time, the UART will start listening for an initial character. After being identified,
it will automatically adjust S2[MSBF], C3[TXINV], and S2[RXINV]. The software must
then receive and process an answer to reset. Upon processing the answer to reset, the
software must write to set C2[RE] = 0 and C2[TE] = 0. The software should then adjust
7816 specific and UART generic parameters to match and configure data that was
received during the answer on reset period. After the new settings have been
programmed, including the new baud rate and C7816[TTYPE], C2[RE] and C2[TE] can
be reenabled as required.
38.9.1.1 Transmission procedure for (C7816[TTYPE] = 0)
When the protocol selected is C7816[TTYPE] = 0, it is assumed that the software has a
prior knowledge of who should be transmitting and receiving. Therefore, no mechanism
is provided for automated transmission/receipt control. The software must monitor
S1[TDRE], or configure for an interrupt, and provide additional data for transmission, as
appropriate. Additionally, software should set C2[TE] = 1 and control TXDIR whenever
it is the UART's turn to transmit information. For ease of monitoring, it is suggested that
only data be transmitted until the next receiver/transmit switchover is loaded into the
transmit buffer.
38.9.1.2 Transmission procedure for (C7816[TTYPE] = 1)
When the protocol selected is C7816[TTYPE] = 1, data is transferred in blocks. Before
starting a transmission, the software must write the size, in number of bytes, for the
Information Field portion of the block into TLEN. If a CRC is being transmitted for the
block, the value in TLEN must be one more than the size of the information field. The
software must then set C2[TE] = 1 and C2[RE] = 1. The software must then monitor
S1[TDRE]/interrupt and write the prologue, information, and epilogue field to the
transmit buffer. TLEN automatically decrements, except for prologue bytes and the final
epilogue byte. When the final epilogue byte has been transmitted, the UART
automatically clears C2[TE] and C3[TXDIR] to 0, and the UART automatically starts
capturing the response to the block that was transmitted. After the software has detected
the receipt of the response, the transmission process must be repeated as needed with
sufficient urgency to ensure that the block wait time and character wait times are not
violated.
38.9.2 Initialization sequence (non ISO-7816)
To initiate a UART transmission:
KL27 Sub-Family Reference Manual , Rev. 5, 01/2016
Freescale Semiconductor, Inc.
739
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