Motorola DSP56012 - Manual (Page 201)

Serial Audio Interface
Serial Audio Interface Programming Model
MOTOROLA DSP56012 User’s Manual 6-23
condition. TLDE is cleared by hardware reset and software reset, when the DSP is in
the Stop state, and when all transmitters are disabled (T2EN, T1EN, and T0EN
cleared).
6.3.4.15 TCS Transmitter Right Data Empty (TRDE)—Bit 15
Transmitter Right Data Empty (TRDE) is a read-only status bit that, in conjunction
with TLDE, indicates the status of the enabled transmit data registers. TRDE is set
when the left data words (as indicated by the TLRS bit in TCS) are simultaneously
transferred from the transmit data registers to the transmit shift registers in the
enabled transmitters. This indicates that the transmit data registers are now free to be
loaded with the right data words. Since audio data samples are composed of left and
right data words that are transmitted alternately, normal operation of the
transmitters is achieved when only one of the status bits (TLDE or TRDE) is set at a
time. A transmit underrun condition is indicated when both TLDE and TRDE are set.
TRDE is cleared when the DSP writes to the transmit data register of the enabled
transmitters, provided that
When a transmit underrun
condition occurs the previous data (which is still present in the
data registers) will be re-transmitted. In this case, TRDE is cleared by first reading the
TCS register, followed by writing the transmit data registers of the enabled
transmitters. If TXIE is set, an interrupt request will be issued when TRDE is set. The
vector of the interrupt request will depend on the state of the transmit underrun
condition. The TRDE is cleared by hardware and software reset, when the DSP is in
the Stop state, and when all transmitters are disabled (T2EN, T1EN and T0EN
cleared).
6.3.5 SAI Transmit Data Registers (TX2, TX1 and TX0)
The three Transmit data registers (TX2, TX1, and TX0) are each 24 bits wide. Data to
be transmitted is written to these registers and is automatically transferred to the
associated shift register after the last bit is shifted out. The transmit data registers
should be written with left channel and right channel data alternately. The first word
to be transmitted, after enabling the operation of the respective transmitter, will be
the left channel word.
(TLDE TRDE
⊕
1). =
(TLDE TRDE
•
1), =