Companding (Compressing and Expanding) Data
2-5
McBSP Operation
SPRU592E
Figure 2
−
3.
µ
-Law Transmit Data Companding Format
µ
-law format in DXR1
00
Value
1
−
0
15
−
2
For transmission using A-law compression, make sure the 13 data bits are
left-justified in DXR1, with the remaining three low-order bits filled with 0s as
shown in Figure 2
Figure 2
−
4. A-Law Transmit Data Companding Format
000
2
−
0
Value
15
−
3
A-law format in DXR1
2.2.2 Capability to Compand Internal Data
If the McBSP is otherwise unused (the serial port transmit and receive sections
are reset), the companding hardware can compand internal data. This can be
used to:
-
Convert linear to the appropriate
µ
-law or A-law format.
-
Convert
µ
-law or A-law to the linear format.
-
Observe the quantization effects in companding by transmitting linear
data, and compressing and re-expanding this data. This is useful only if
both XCOMPAND and RCOMPAND enable the same companding format.
5 shows two methods by which the McBSP can compand internal
data. Data paths for these two methods are used to indicate:
-
When both the transmit and receive sections of the serial port are reset,
DRR1 and DXR1 are connected internally through the companding logic.
Values from DXR1 are compressed, as selected by XCOMPAND, and
then expanded, as selected by RCOMPAND. Note that RRDY and XRDY
bits are not set. However, data is available in DRR1 within four McBSP
internal input clock cycles after being written to DXR1. This method is
indicated as (1) in Figure 2
The advantage of this method is its speed. The disadvantage is that there
is no synchronization available to the CPU and the DMA controller to
control the flow. Note that DRR1 and DXR1 are internally connected if the
(X/R)COMPAND bits are set to 10b or 11b (compand using
µ
-law or
A-law).
Содержание TMS320VC5509
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