Motorola DSP56012 - Manual (Page 199)

Serial Audio Interface
Serial Audio Interface Programming Model
MOTOROLA DSP56012 User’s Manual 6-21
register, the last bit is transmitted eight times. When TDWE is set, the first bit is
transmitted 8 times and then the 24-bit data word from the transmit data register is
transmitted. The TDWE bit is ignored if TWL[1:0] are set for a word length other than
32 bits (see Figure 6-14). The TDWE bit is cleared during hardware reset and
software reset.
6.3.4.11 TCS Transmitter Interrupt Enable (TXIE)—Bit 11
When the read/write Transmitter Interrupt Enable (TXIE) control bit is set,
transmitter interrupts for both left and right data words are enabled, and the DSP is
interrupted if either the TLDE or TRDE status bit is set. When TXIE is cleared,
transmitter interrupts are disabled. However, the TLDE and TRDE bits still signal the
transmit data register empty conditions. Clearing TXIE will mask a pending
transmitter interrupt only after a one-instruction-cycle delay. If TXIE is cleared in a
long interrupt service routine, it is recommended that at least one other instruction
should be inserted between the instruction that clears TXIE and the RTI instruction at
the end of the interrupt service routine.
There are three different transmit data interrupts that have separate interrupt
vectors:
1. Left Channel Transmit interrupt is generated when TXIE = 1, TLDE = 1, and
TRDE = 0. The transmit data registers should be loaded with the left data
words.
2. Right Channel Transmit interrupt is generated when TXIE = 1, TLDE = 0, and
TRDE = 1. The transmit data registers should be loaded with the right data
words.
3. Transmit interrupt with exception (underrun) is generated when TXIE = 1,
TLDE = 1, and TRDE = 1. This means that old data is being retransmitted.
Figure 6-14 Transmitter Data Word Expansion (TDWE) Programming
SDI
WST
SDO
1 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
SCKT
Left Right
TDWE = 0
TDWE = 1
1 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
AA0440k