Introduction; Ssi Operating Modes - Motorola DSP56156 Manual

8.1

INTRODUCTION

The DSP56156 contains two identical Synchronous Serial Interfaces (SSI's) named SSI0
and SSI1. This section describes both. In cases where the text or a figure applies equally
to both SSI's, they will be referred to as the SSI. In cases where the information differs
between the SSI's such as when pin numbers are mentioned, control addresses are men-
tioned or the operation affects only one of the two SSI's like a personal reset, the SSI will
be referred to as SSIx meaning SSI0 or SSI1 – whichever applies.
The SSI is a full duplex serial port which allows the DSP to communicate with a variety of
serial devices including one or more industry standard codecs, other DSPs, or micropro-
cessors and peripherals. A selectable logarithmic compression and expansion is available
for easier interface with PCM monocircuits and PCM highways. The SSI interface consists
of independent transmitter and receiver sections and a common SSI clock generator.
8.2

SSI OPERATING MODES

The SSI has several basic operating modes. These modes can be programmed by sev-
eral bits in the SSI Control registers. The Table 8-1 below lists the SSI operating modes:
The transmit and receive sections of this interface may be synchronous or asynchronous;
that is, the transmitter and the receiver may use common clock and synchronization sig-
nals or they may have independent frame sync signals but the same bit clock. The SYN
bit in SSI Control Register B selects synchronous or asynchronous operation. Since the
SSI is designed to operate either synchronously or asynchronously, separate receive and
transmit interrupts are provided.
Normal or network protocol may also be selected. For normal protocol the SSI functions
with one data word of I/O per frame. For network protocol, 2 to 32 data words of I/O may
be used per frame. Network mode is used in Time Division Multiplexed (TDM) networks
of codecs or DSPs. These distinctions result in the basic operating modes which allow the
SSI to communicate with a wide variety of devices.
MOTOROLA SYNCHRONOUS SERIAL INTERFACE (SSI0 and SSI1)
INTRODUCTION
Table 8-1 SSI Operating Modes
TX, RX Sections Serial Clock
Asynchronous Continuous
Synchronous Continuous
Synchronous Continuous
Asynchronous Continuous
Protocol
Normal
Normal
Network
Network
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