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ST90158 - SERIAL COMMUNICATIONS INTERFACE (SCI)
9.5 SERIAL COMMUNICATIONS INTERFACE (SCI)
9.5.1 Introduction
The Serial Communications Interface (SCI) offers
full-duplex serial data exchange with a wide range
of external equipment. The SCI offers four operat-
ing modes: Asynchronous, Asynchronous with
synchronous clock, Serial expansion and Syn-
chronous.
The SCI offers the following principal features:
s
Full duplex synchronous and asynchronous
operation.
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Transmit, receive, line status, and device
address interrupt generation.
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Integral Baud Rate Generator capable of
dividing the input clock by any value from 2 to
216-1 (16 bit word) and generating the internal
16X data sampling clock for asynchronous
operation or the 1X clock for synchronous
operation.
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Fully programmable serial interface:
– 5, 6, 7, or 8 bit word length.
– Even, odd, or no parity generation and detec-
tion.
– 0, 1, 1.5, 2, 2.5, 3 stop bit generation.
– Complete status reporting capabilities.
– Line break generation and detection.
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Programmable address indication bit (wake-up
bit) and user invisible compare logic to support
multiple microcomputer networking. Optional
character search function.
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Internal diagnostic capabilities:
– Local loopback for communications link fault
isolation.
– Auto-echo for communications link fault isola-
tion.
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Separate interrupt/DMA channels for transmit
and receive.
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In addition, a Synchronous mode supports:
– High speed communication
– Possibility of hardware synchronization (RTS/
DCD signals).
– Programmable polarity and stand-by level for
data SIN/SOUT.
– Programmable active edge and stand-by level
for clocks CLKOUT/RXCL.
– Programmable active levels of RTS/DCD sig-
nals.
– Full Loop-Back and Auto-Echo modes for DA-
TA, CLOCKs and CONTROLs.
Figure 75. SCI Block Diagram
TRANSMIT
BUFFER
REGISTER
SHIFT
TRANSMIT
REGISTER
SHIFT
RECEIVER
FUNCTION
ALTERNATE
REGISTER
COMPARE
ADDRESS
REGISTER
BUFFER
RECEIVER
DMA
CONTROLLER
CLOCK and
BAUD RATE
GENERATOR
ST9 CORE BUS
SOUT
TXCLK/CLKOUT RXCLK
SIN
VA00169A
Frame Control
and STATUS
DMA
CONTROLLER
RTS
DCD
SDS
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