Sci I/O Signals; Introduction - Motorola DSP56305 User Manual

8.1

INTRODUCTION

The DSP56305's Serial Communications 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 (up to 10.0 Mbps for an
80 MHz clock). 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 DSP56305 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
General Purpose I/O (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 when one or more of the SCI signals is programmed as an SCI
signal.
MOTOROLA DSP56305 User's Manual
Serial Communication Interface (SCI)
Introduction
8-3