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(DLB)
From CPU or EDMA controller
DX
DR
To CPU or
EDMA controller
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DRR
RJUST
DXR
RBR
XSR
RSR
Architecture
1225
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Multichannel Buffered Serial Port (McBSP)
Table 25-12. Justification of Expanded Data in DRR
RJUST Bit in SPCR
DRR Bits
31
16
15
0
00
0
LAW16
01
sign
LAW16
10
LAW16
0
11
Reserved
25.2.8.1 Companding Internal Data
If the McBSP is unused, the companding hardware can compand internal data. This hardware can be
used to:
•
Convert linear data to the appropriate
μ
-law or A-law format.
•
Convert
μ
-law or A-law data 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.
shows the method by which the McBSP can compand internal data. The data path is
indicated by the (DLB) arrow. The McBSP is enabled in digital loopback (DLB) mode with companding
appropriately enabled by the RCOMPAND and XCOMPAND bits. Receive and transmit interrupts (RINT
when RINTM = 0 and XINT when XINTM = 0) or synchronization events (REVT and XEVT) allow
synchronization of the CPU or the EDMA controller to these conversions, respectively. The time for this
companding depends on the serial bit rate selected.
Figure 25-36. Companding of Internal Data
25.2.8.2 Bit Ordering
Normally, all transfers on the McBSP are sent and received with the MSB first. However, certain 8-bit data
protocols (that do not use companded data) require the LSB to be transferred first. By setting the
(R/X)COMPAND = 01b in (R/X)CR, the bit ordering of 8-bit elements is reversed (LSB first) before being
sent to the serial port. Like the companding feature, this feature is enabled only if the appropriate
(R/X)WDLEN1/2 bit is cleared to 0, indicating that 8-bit elements are to be serially transferred. A 32-bit bit
reversal feature is also available, as shown in