0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
CLK
Frame
sync
Frame sync:
(0 bit delay)
Frame sync:
(1 bit delay)
Frame sync:
(2 bit delay)
Slot 0
Slot 1
Slot 0
Slot 1
Slot 0
Slot 1
1106
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Multichannel Audio Serial Port (McASP)
When ASYNC = 0, the transmit and receive sections must share some common settings, since they both
use the same clock and frame sync signals:
•
DITEN = 0 in DITCTL (TDM mode is enabled)
•
The total number of bits per frame must be the same (that is, RSSZ × RMOD must equal XSSZ ×
XMOD)
•
Both transmit and receive should either be specified as burst or TDM mode, but not mixed
•
The settings in ACLKRCTL are irrelevant
•
RCLK is an inverted version of XCLK (note the inversion on the multiplexer labeled “ASYNC” shown in
•
FSXM must match FSRM
•
FXWID must match FRWID
For all other settings, the transmit and receive sections may be programmed independently.
24.0.21.1.6 Asynchronous Transmit and Receive Operation (ASYNC = 1)
When ASYNC = 1 in ACLKXCTL, the transmit and receive sections operate completely independently and
have separate clock and frame sync signals (
, and
). The events
generated by each section come asynchronously.
24.0.21.2 Transfer Modes
24.0.21.2.1 Burst Transfer Mode
The McASP supports a burst transfer mode, which is useful for nonaudio data such as passing control
information between two CPUs. Burst transfer mode uses a synchronous serial format similar to the TDM
mode. The frame sync generation is not periodic or time-driven as in TDM mode, but data driven, and the
frame sync is generated for each data word transferred.
When operating in burst frame sync mode (
), as specified for transmit (XMOD = 0 in
AFSXCTL) and receive (RMOD = 0 in AFSRCTL), one slot is shifted for each active edge of the frame
sync signal that is recognized. Additional clocks after the slot and before the next frame sync edge are
ignored.
In burst frame sync mode, the frame sync delay may be specified as 0, 1, or 2 serial clock cycles. This is
the delay between the frame sync active edge and the start of the slot. The frame sync signal lasts for a
single bit clock duration (FRWID = 0 in AFSRCTL, FXWID = 0 in AFSXCTL).
For transmit, when generating the transmit frame sync internally, the frame sync begins when the previous
transmission has completed and when all the XBUF
n
(for every serializer set to operate as a transmitter)
has been updated with new data.
For receive, when generating the receive frame sync internally, frame sync begins when the previous
transmission has completed and when all the RBUF
n
(for every serializer set to operate as a receiver) has
been read.
Figure 24-23. Burst Frame Sync Mode