MC9S12T64 Datasheet, PDF (439/608 Pages) Motorola, Inc – Specification

Freescale Semiconductor, Inc.
Serial Communications Interface (SCI)
Functional Description
shift register. The transmit shift register then shifts a frame out through
the TX output signal, after it has prefaced it with a start bit and
appended it with a stop bit. The SCI data registers (SCIxDRH and
SCIxDRL) are the write-only buffers between the internal data bus and
the transmit shift register.
The SCI also sets a flag, the transmit data register empty flag (TDRE),
every time it transfers data from the buffer (SCIxDRH/L) to the
transmitter shift register.The transmit driver routine may respond to this
flag by writing another byte to the Transmitter buffer
(SCIxDRH/SCIxDRL), while the shift register is still shifting out the first
byte.
To initiate an SCI transmission:
9. Configure the SCI:
a. Select a baud rate. Write this value to the SCI baud registers
(SCIxBDH/L) to begin the baud rate generator. Remember
that the baud rate generator is disabled when the baud rate is
zero. Writing to the SCIxBDH has no effect without also writing
to SCIxBDL.
b. Write to SCIxCR1 to configure word length, parity, and other
configuration bits (LOOPS, RSRC, M, WAKE, ILT, PE, PT).
c. Enable the transmitter, interrupts, receive, and wake up as
required, by writing to the SCIxCR2 register bits (TIE, TCIE,
RIE, ILIE, TE, RE, RWU, SBK). A preamble or idle character
will now be shifted out of the transmitter shift register.
10. Transmit Procedure for Each Byte:
a. Poll the TDRE flag by reading the SCIxSR1 or responding to
the TDRE interrupt. Keep in mind that the TDRE bit resets to
one.
b. If the TDRE flag is set, write the data to be transmitted to
SCIxDRH/L, where the ninth bit is written to the T8 bit in
SCIxDRH if the SCI is in 9-bit data format. A new transmission
will not result until the TDRE flag has been cleared.
11. Repeat step 2 for each subsequent transmission.
Serial Communications Interface (SCI)
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MC9S12T64Revision 1.1.1