Section 25 Audio Codec Interface (HAC)
Rev.1.00 Dec. 13, 2005 Page 975 of 1286
REJ09B0158-0100
25.5.2 Transmitter
The HAC transmitter outputs serial audio data on the HAC_SDOUT pin, synchronous to
HAC_BIT_CLK. The transmitter sets the tag bits in slot 0 to indicate which slots in the current
frame contain valid data. It loads data slots to the current TX frame in response to the
corresponding slot request bits from the previous RX frame.
The transmitter supports data only in slots 1 to 4. The TX buffer holds data that has been
transferred using PIO or DMA, and sets the corresponding status bit. It is possible to write 20-bit
data within a 32-bit register using PIO.
In the case of a TX underrun, the HAC will transmit the current TX buffer data until the next data
arrives.
25.5.3 DMA
The HAC supports DMA transfer for slots 3 and 4 of both the RX and TX frames. Specify the slot
data size for DMA transfer, 16 or 20 bits, with the DMARX16 and DMATX16 bits in HACACR.
When the data size is 20 bits, transfer of data slots 3 and 4 requires two local bus access cycles.
Since each of the receiver and transmitter has its DMA request, the stereo mode generates a DMA
request for slots 3 and 4 separately. The mono mode generates a DMA request for just one slot.
When the data size is 16 bits, data from slots 3 and 4 are packed into a single 32-bit quantity (left
data and right data are in PCML), which requires only one local bus access cycle.
It may be necessary to halt a DMA transfer before the end count is reached, depending on system
applications. If so, clear the corresponding DMA bit in HACACR to 0 (DMA disabled). To
resume a DMA transfer, reprogram the DMAC and then set the corresponding DMA bit to 1
(DMA enabled).
25.5.4 Interrupts
Interrupts can be used for flag events from the receiver and transmitter. Make the setting for each
interrupt in the corresponding interrupt enable register. Interrupts include a request to the CPU to
read/write slot data, overrun and underrun. To get the interrupt source, read the status register.
Writing 0 to the bit will clear the corresponding interrupt.
Содержание SH7780 Series
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