Motorola DSP56303 User Manual page 171

Table 7-4. ESSI Control Register B (CRB) Bit Definitions (Continued)
Bit Number Bit Name
4 SCD2
3 SCD1
2 SCD0
1 OF1
0 OF0
Reset Value
0 Serial Control Direction 2
Controls the direction of the SC2 I/O signal. When SCD2 is set, SC2 is an
output; when SCD2 is cleared, SC2 is an input.
NOTE: Programming the ESSI to use an internal frame sync (that is,
SCD2 = 1 in CRB) causes the SC2 and SC1 signals to be programmed as
outputs. However, if the corresponding multiplexed pins are programmed
by the Port Control Register (PCR) to be GPIOs, the GPIO Port Direction
Register (PRR) chooses their direction. The ESSI uses an external frame
sync if GPIO is selected. To assure correct operation, either program the
GPIO pins as outputs or configure the pins in the PCR as ESSI signals.
The default selection for these signals after reset is GPIO. This note
applies to both ESSI0 and ESSI1.
0 Serial Control Direction 1
In Synchronous mode (SYN = 1) when transmitter 2 is disabled (TE2 = 0),
or in Asynchronous mode (SYN = 0), SCD1 controls the direction of the
SC1 I/O signal. When SCD1 is set, SC1 is an output; when SCD1 is
cleared, SC1 is an input. When TE2 is set, the value of SCD1 is ignored
and the SC1 signal is always an output.
0 Serial Control Direction 0
In Synchronous mode (SYN = 1) when transmitter 1 is disabled (TE1 = 0),
or in Asynchronous mode (SYN = 0), SCD0 controls the direction of the
SC0 I/O signal. When SCD0 is set, SC0 is an output; when SCD0 is
cleared, SC0 is an input. When TE1 is set, the value of SCD0 is ignored
and the SC0 signal is always an output.
0 Serial Output Flag 1
In Synchronous mode (SYN = 1), when transmitter 2 is disabled (TE2 = 0),
the SC1 signal is configured as ESSI flag 1. When SCD1 is set, SC1 is an
output. Data present in bit OF1 is written to SC1 at the beginning of the
frame in Normal mode or at the beginning of the next time slot in Network
mode.
0 Serial Output Flag 0
In Synchronous mode (SYN = 1), when transmitter 1 is disabled (TE1 = 0),
the SC0 signal is configured as ESSI flag 0. When SCD0 is set, the SC0
signal is an output. Data present in Bit OF0 is written to SC0 at the
beginning of the frame in Normal mode or at the beginning of the next time
slot in Network mode.
Enhanced Synchronous Serial Interface (ESSI)
ESSI Programming Model
Description
7-23