Signal Descriptions
MOTOROLA
Enhanced Synchronous Serial Interface (ESSI)
12-7
Preliminary
12
signal is used for the receive clock I/O. In synchronous mode, this signal is used as the
transmitter data out signal for transmit shift register TX1 or for serial flag I/O. A typical
application of serial flag I/O would be multiple device selection for addressing in codec
systems.
If SC0 is configured as a serial flag signal or receive clock signal, its direction is
determined by the Serial Control Direction 0 (SCD0) bit in the ESSI Control Register 4
(SCR4). When configured as an output, SC0 may be used either as the serial Output Flag 0
(OF0) or as a receive shift register clock output. If the SC0 is used as the serial OF0, its
value is determined by the value of the serial OF0 bit in the SCR4 register.
If SC0 is an input, this signal may be used either as serial Input Flag 0 (IF0) or as a
Receive Shift Register (RSR) clock input. If SC0 is used as serial Input Flag 0, it controls
the state of the serial Input Flag 0 bit in the ESSI Status Register (ESSR). When SC0 is
configured as a transmit data signal, it is always an output signal regardless of the SCD0
bit value. SC0 is fully synchronized with the other transmit data signals, STD and SC1.
Note:
The ESSI can operate with more than one active transmitter only in the
Synchronous mode.
12.3.2.3 ESSI Receive Frame Sync (SC1)
The function of this signal is determined by the programmer selecting either Synchronous
or Asynchronous modes, according to Table 12-4. In the Asynchronous mode, such as a
single codec with asynchronous transmit and receive, the SC1is the receiver frame sync
I/O. In the Synchronous mode, the SC1 is used for the transmitter data out signal of
Transmit Shift Register (TXSR2), for the transmitter 0 drive-enable signal, or for serial
flag I/O.
When used as serial flag I/O, SC1operates like SC0. SC0 and SC1 are independent flags,
but they may be used together for multiple serial device selection. SC0 and SC1 can be
used without being encoded to select up to two codecs. They may also be decoded
externally to select up to four codecs. If the SC1 is configured as a serial flag signal, its
direction is determined by the SCD1 bit in SCR4 register.
If the SC1 is configured as a serial flag or receive frame sync signal, its direction is
determined by the Serial Control Direction 1 (SCD1) bit in the SCR4 register.
When configured as an output, the SC1 signal can be used as a serial output flag, as the
transmitter 0 drive-enable signal for the purpose to control an external high-drive buffer,
or as the receive frame sync signal output. If SC1 is used as serial output flag 1, its value is
determined by the value of the serial Output Flag 1 (OF1) bit in the SCR4 register.