CP3BT10 Datasheet, PDF (96/210 Pages) National Semiconductor (TI) – Reprogrammable Connectivity Processor with Bluetooth and USB Interfaces

The transmitter only drives data on the STD pin during slots
which have been assigned to this interface. During all other
slots, the STD output is in high-impedance mode, and data
can be driven by other devices. The assignment of slots to
the transmitter is specified by the Transmit Slot Assignment
bits (TXSA) in the ATCR register. It can also be specified
whether the data to be transmitted is transferred from the
transmit FIFO or the corresponding DMA transmit register.
There is one DMA transmit register (ATDRn) for each of the
maximum four data slots. Each slot can be configured inde-
pendently.
On the receiver side, only the valid data bits which were re-
ceived during the slots assigned to this interface are copied
into the receive FIFO or DMA registers. The assignment of
slots to the receiver is specified by the Receive Slot Assign-
ment bits (RXSA) in the ATCR register. It can also be spec-
ified whether the received data is copied into the receive
FIFO or into the corresponding DMA receive register. There
is one DMA receive register (ARDRn) for each of the maxi-
mum four data slots. Each slot may be configured individu-
ally.
Figure 32 shows the frame timing while operating in network
mode with four slots per frame, slot 1 assigned to the inter-
face, and a long frame sync interval.
Long Frame Sync
(SFS/SRFS)
DMA Support
If DMA support is enabled for a receive slot n (RXDSA0 =
1), all data received in this slot is only transferred from the
ARSR into the corresponding DMA receive register
(ARDRn). A DMA request is asserted when the ARDRn reg-
ister is full.
If DMA is enabled for a transmit slot n (TXDSAn = 1), all data
to be transmitted in slot n are read from the corresponding
DMA transmit register (ATDRn). A DMA request is asserted
to the DMA controller when the ATDRn register is empty.
Figure 33 illustrates the data flow for IRQ and DMA support
in network mode, using four slots per frame and DMA sup-
port enabled for slots 0 and 1 in receive and transmit direc-
tion.
SRD
ARSR
DMA Slot
Assignment
Slot ^{1 data}
Slot _{2 and 3 data}
ARDR 0
ARDR 1
DMA
Request 1
DMA
Request 3
ARDR 2
ARDR 3
RX
IRQ
FIFO
Shift Data
(STD/SRD)
Data
(ignored)
Data
(valid)
High-impedance
Data
(ignored)
Slot0
Slot1
Unused Slots
Frame
DS055
Figure 32. Network Mode Frame
IRQ Support
If DMA is not enabled for a receive slot n (RXDSAn = 0), all
data received in this slot is loaded into the receive FIFO. An
IRQ is asserted as soon as the number of data bytes or
words in the receive FIFO is greater than a configured warn-
ing limit.
If DMA is not enabled for a transmit slot n (TXDSAn = 0), all
data to be transmitted in this slot are read from the transmit
FIFO. An IRQ is asserted as soon as the number data bytes
or words available in the transmit FIFO is equal or less than
a configured warning limit.
STD
ATSR
DMA Slot
Assignment
Slot ^{1 data}
Slot _{2 and 3 data}
ATDR 0
ATDR 1
DMA
Request 0
DMA
Request 2
ATDR 2
ATDR 3
TX
FIFO
IRQ
DS056
Figure 33. IRQ/DMA Support in Network Mode
If the interface operates in synchronous mode, the receiver
uses the transmit bit clock (SCK) and transmit frame sync
signal (SFS). This allows the pins used for the receive bit
clock (SRCLK) and receive frame sync (SRFS) to be used
as additional frame sync signals in network mode. The extra
frame sync signals are useful when the audio interface com-
municates to more than one codec, because codecs typical-
ly start transmission immediately after the frame sync pulse.
The SRCLK pin is driven with a frame sync pulse at the be-
ginning of the second slot (slot 1), and the SRFS pin is driv-
en with a frame sync pulse at the beginning of slot 2.
Figure 34 shows a frame timing diagram for this configura-
tion, using the additional frame sync signals on SRCLK and
SRFS to address up to three devices.
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