Serial Communication Interface (SCI)
Introduction
MOTOROLA
DSP56309UM/D 8-3
8.1
INTRODUCTION
The DSP56309 serial communication interface (SCI) provides a full-duplex port for serial
communication to other DSPs, microprocessors, or peripherals such as modems. The SCI
interfaces without additional logic to peripherals that use TTL-level signals. With a small
amount of additional logic, the SCI can connect to peripheral interfaces that have
non-TTL level signals, such as the RS232C, RS422, etc.
This interface uses three dedicated signals: transmit data (TXD), receive data (RXD), and
SCI serial clock (SCLK). It supports industry-standard asynchronous bit rates and
protocols, as well as high-speed synchronous data transmission. The asynchronous
protocols supported by the SCI include a multidrop mode for master/slave operation
with wakeup on idle line and wakeup on address bit capability. This mode allows the
DSP56309 to share a single serial line efficiently with other peripherals.
The SCI consists of separate transmit and receive sections that can operate
asynchronously with respect to each other. A programmable baud-rate generator
provides the transmit and receive clocks. An enable vector and an interrupt vector have
been included so that the baud-rate generator can function as a general purpose timer
when it is not being used by the SCI, or when the interrupt timing is the same as that
used by the SCI.
8.2
SCI I/O SIGNALS
Each of the three SCI signals (RXD, TXD, and SCLK) can be configured as either a GPIO
signal or as a specific SCI signal. Each signal is independent of the others. For example, if
only the TXD signal is needed, the RXD and SCLK signals can be programmed for GPIO.
However, at least one of the three signals must be selected as an SCI signal to release the
SCI from reset.
SCI interrupts can be enabled by programming the SCI control registers before any of
the SCI signals are programmed as SCI functions. In this case, only one transmit
interrupt can be generated because the transmit data register is empty. The timer and
timer interrupt operate regardless of how the SCI pins are configuredÑeither as SCI or
GPIO.
Содержание DSP56309
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