Motorola DSP56301 - Manual (Page 200)

ESSI Enhancements
7 -2 DSP56301 User’s Manual
Note: This synchronous interface should not be confused with the asynchronous channels
mode of the ESSI, in which separate clocks are used for the receiver and
transmitter. In that mode, the ESSI is still a synchronous device because all
transfers are synchronized to these clocks. Pin notations for the generic ESSI refer
to the analogous pin of ESSI0 (
PCx ) and ESSI1 ( PDx ).
Additional synchronization signals delineate the word frames. The Normal mode of operation
transfers data at a periodic rate, one word per period. The Network mode is similar in that it is
also for periodic transfers; however, it supports up to 32 words (time slots) per period. The
Network mode can be used to build time division multiplexed (TDM) networks. In contrast,
the On-Demand mode is for nonperiodic transfers of data. This mode, which offers a subset of
the Motorola Serial Peripheral Interface (SPI) protocol, can transfer data serially at high speed
when the data become available. Since each ESSI unit can be configured with one receiver
and three transmitters, the two units can be used together for surround sound applications
(which need two digital input channels and six digital output channels).
7.1 ESSI Enhancements
The DSP56000 SSI is enhanced in the following ways to make the ESSI:
n Network enhancements
— Time slot mask registers (receive and transmit)
— End-of-frame interrupt
— Drive enable signal (used with transmitter 0)
n Audio enhancements
— Three transmitters per ESSI (for six-channel surround-sound)
n General enhancements
— Can trigger DMA interrupts (receive or transmit)
— Separate exception enable bits
n Other changes
— One divide-by-2 step is removed from the internal clock source chain
— The CRA[PSR] bit definition is reversed
— Gated-Clock mode is not available