Motorola DSP56309 User Manual page 172

Enhanced Synchronous Serial Interface (ESSI)
ESSI Data and Control Signals
7.3.5 Serial Control Signal (SC1)
SC01 is a serial control signal for ESSI0, and SC11 is a serial control signal for ESSI1. They
are referred to collectively as SC1.
The function of this signal is determined by selecting either synchronous or
asynchronous mode; see Table 7-4 on page 7-24. In asynchronous mode (such as a single
codec with asynchronous transmit and receive), SC1 is the receiver frame sync I/O. In
synchronous mode, SC1 is used for the transmitter data out signal of transmit shift
register TX2, for the drive enable transmitter 0 signal, or for serial flag SC1.
When used as a serial flag signal, SC1 operates like the previously described SC0. SC0
and SC1 are independent flags but can be used together for multiple serial device
selection. SC0 and SC1 can be used unencoded to select up to two codecs or can be
decoded externally to select up to four codecs.
If SC1 is configured as a serial flag signal, its direction is determined by the SCD1 bit in
the CRB. When configured as an output, its value is determined by the value of the serial
output flag1 (OF1) bit in the CRB. When configured as an input, SC0 controls the stated
serial input flag 1 (IF1) bits in SSISR.
When SC1 is configured as a transmit data signal, it is always an output signal
regardless of the SCD1 bit value. As an output, it is fully synchronized with the other
ESSI transmit data signals (STD and SC0).
In asynchronous mode, SC1 is configured as the receive frame sync. The direction of SC1
in this mode is determined by SCD1.
SC1 can be programmed as a GPIO signal (P1) when the ESSI SC1 function is not being
used.
Table 7-1 summarizes ESSI clock sources, whether synchronous or asynchronous, and
shows the bit settings for the signals involved.
MOTOROLA DSP56309UM/D 7-7