MC68HC16Z1CAG16 Datasheet, PDF (235/500 Pages) Freescale Semiconductor, Inc – M68HC16Z Series users manual

Freescale Semiconductor, Inc.
9.4.2 SCI Pins
Two unidirectional pins, TXD (transmit data) and RXD (receive data), are associated
with the SCI. TXD can be used by the SCI or for general-purpose I/O. TXD function is
controlled by PQSPA7 in the port QS pin assignment register (PQSPAR) and TE in
SCI control register 1 (SCCR1). The receive data (RXD) pin is dedicated to the SCI.
9.4.3 SCI Operation
The SCI can operate in polled or interrupt-driven mode. Status flags in SCSR reflect
SCI conditions regardless of the operating mode chosen. The TIE, TCIE, RIE, and ILIE
bits in SCCR1 enable interrupts for the conditions indicated by the TDRE, TC, RDRF,
and IDLE bits in SCSR, respectively.
9.4.3.1 Definition of Terms
• Bit-Time — The time required to transmit or receive one bit of data, which is equal
to one cycle of the baud frequency.
• Start Bit — One bit-time of logic zero that indicates the beginning of a data frame.
A start bit must begin with a one-to-zero transition and be preceded by at least
three receive time samples of logic one.
• Stop Bit — One bit-time of logic one that indicates the end of a data frame.
• Frame — A complete unit of serial information. The SCI can use 10-bit or 11-bit
frames.
• Data Frame — A start bit, a specified number of data or information bits, and at
least one stop bit.
• Idle Frame — A frame that consists of consecutive ones. An idle frame has no
start bit.
• Break Frame — A frame that consists of consecutive zeros. A break frame has
no stop bits.
9.4.3.2 Serial Formats
All data frames must have a start bit and at least one stop bit. Receiving and transmit-
ting devices must use the same data frame format. The SCI provides hardware sup-
port for both 10-bit and 11-bit frames. The M bit in SCCR1 specifies the number of bits
per frame.
The most common data frame format for NRZ serial interfaces is one start bit, eight
data bits (LSB first), and one stop bit; a total of ten bits. The most common 11-bit data
frame contains one start bit, eight data bits, a parity or control bit, and one stop bit.
Ten-bit and 11-bit frames are shown in Table 9-4.
M68HC16 Z SERIES
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