Texas Instruments TMS320C6745 DSP - Definition of Frame and Frame Sync Width

Slot 0 Slot 1
Slot
Frame
Frame sync width
FS
AXR[n]
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SPRUH91D–March 2013–Revised September 2016
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Multichannel Audio Serial Port (McASP)
The third basic element of a synchronous serial interface is the frame synchronization signal, also referred
to as frame sync in this chapter.
Frame A frame contains one or multiple slots, as determined by the desired protocol. Figure 24-14 shows an example frame
of data and the frame definitions. Figure 24-14 does not specify whether the frame sync (FS) is for transmit (AFSX)
or receive (AFSR) because the definitions of terms apply to both receive and transmit interfaces. In operation, the
transmitter uses AFSX and the receiver uses AFSR. Optionally, the receiver can use AFSX as the frame sync when
the transmitter and receiver of the McASP are configured to operate synchronously.
This section only shows the generic definition of the frame sync. See Section 24.0.18.1, Section 24.0.18.2,
and Section 24.0.21.2.1 for details on the frame sync formats required for the different transfer modes and
protocols (burst mode, TDM mode and I2S format, DIT mode and S/PDIF format).
Figure 24-14. Definition of Frame and Frame Sync Width
(1) In this example, there are two slots in a frame, and FS duration of slot length is shown.
Other terms used throughout this chapter:
TDM Time-division multiplexed. See Section 24.0.18.1 for details on the TDM protocol.
DIR Digital audio interface receive. The McASP does not natively support receiving in the S/PDIF format. The McASP
supports I2S format output by an external DIR device.
DIT Digital audio interface transmit. The McASP supports transmitting in S/PDIF format on up to all data pins
configured as outputs.
I2S Inter-IC Sound protocol, commonly used on audio interfaces. The McASP supports the I2S protocol as part of the
TDM mode (when configured as a 2-slot frame).
Slot or
Time Slot
For TDM format, the term time slot is interchangeable with the term slot defined in this section. For DIT format, a
McASP time slot corresponds to a DIT subframe.