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Slot 1
Slot 0
Slot N−1
Slot M
Slot N+1
EDMA event
for slot 0
EDMA event
for slot 1
EDMA event
for slot N − 1
EDMA event
for slot N
EDMA event
for slot N + 1
Slot 1
Slot 2
Slot N
Slot N
EDMA event
for slot 2
EDMA event
for slot M
Active slot
Inactive slot
Slot N−2
Slot 0
Slot M−1
Initialization
period
(A)
EDMA event
for slot N + 2
Initialization
period
(A)
1109
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Multichannel Audio Serial Port (McASP)
If the transmit/receive bit is active, the McASP functions normally during that time slot; otherwise, the
McASP is inactive during that time slot; no update to the buffer occurs, and no event is generated.
Transmit pins are automatically set to a high-impedance state, 0, or 1 during that slot, as determined by
bit DISMOD in SRCTL[n].
shows when the transmit DMA event AXEVT is generated. See
for
details on data ready and the initialization period indication. The transmit DMA event for an active time slot
(slot N) is generated during the previous time slot (slot N - 1), regardless if the previous time slot (slot N -
1) is active or inactive.
During an active transmit time slot (slot N), if the next time slot (slot N + 1) is configured to be active, the
copy from XRBUF[n] to XRSR[n] generates the DMA event for time slot N + 1. If the next time slot (slot
N + 1) is configured to be inactive, then the DMA event will be delayed to time slot M - 1. In this case, slot
M is the next active time slot. The DMA event for time slot M is generated during the first bit time of slot
M - 1.
The receive DMA request generation does not need this capability, since the receive DMA event is
generated after data is received in the buffer (looks back in time). If a time slot is disabled, then no data is
copied to the buffer for that time slot and no DMA event is generated.
Figure 24-24. Transmit DMA Event (AXEVT) Generation in TDM Time Slots
A
See
, step 7a.
24.0.21.2.2.2 Special 384 Slot TDM Mode for Connection to External DIR
The McASP receiver also supports a 384 time slot TDM mode (DIR mode), to support S/PDIF, AES-3,
IEC-60958 receiver ICs whose natural block (block corresponds to McASP frame) size is 384 samples.
The advantage to using the 384 time slot TDM mode is that interrupts may be generated synchronous to
the S/PDIF, AES-3, IEC-60958, such as the last slot interrupt.
The receive TDM time slot register (RTDM) should be programmed to all 1s during reception of a DIR
block. Other TDM functionalities (for example, inactive slots) are not supported (only the slot counter
counts the 384 subframes in a block).
To receive data in the DIR mode, the following pins are typically needed:
•
ACLKR - receive bit clock.
•
AFSR - receive frame sync (or commonly called left/right clock). In this mode, AFSR should be
connected to a DIR which outputs a start of block signal, instead of LRCLK.
•
One or more serial data pins, AXR[n], whose serializers have been configured to receive.
For this special DIR mode, the control registers can be configured just as for TDM mode, except set
RMOD in AFSRCTL to 384 to receive 384 time slots.