Reversing Bit Order: Option To Transfer Lsb First; Two Methods By Which The Mcbsp Can Compand Internal Data - Texas Instruments TMS320VC5501 Reference Manual

Companding (Compressing and Expanding) Data
Figure 2−5. Two Methods by Which the McBSP Can Compand Internal Data
RSR1
DR
(2) (DLB)
DX
2.2.3

Reversing Bit Order: Option to Transfer LSB First

2-6 McBSP Operation
The McBSP is enabled in digital loopback mode with companding
-
appropriately enabled by RCOMPAND and XCOMPAND. Receive and
transmit interrupts (RINT when RINTM = 00b and XINT when
XINTM = 00b) or synchronization events (REVT and XEVT) allow
synchronization of the CPU or the DMA controller to these conversions,
respectively. Here, the time for this companding depends on the serial bit
rate selected. This method is indicated as (2) in Figure 2−5 below.
RBR1
Expand
(1)
Compress
XSR1
Normally, the McBSP transmits or receives all data with the most significant
bit (MSB) first. However, certain 8-bit data protocols (that do not use
companded data) require the least significant bit (LSB) to be transferred first.
If you set XCOMPAND = 01b in XCR2, the bit ordering of 8-bit words is
reversed (LSB first) before being sent from the serial port. If you set
RCOMPAND = 01b in RCR2, the bit ordering of 8-bit words is reversed during
reception. Similar to companding, this feature is enabled only if the appropriate
word length bits are set to 0, indicating that 8-bit words are to be transferred
serially. If either phase of the frame does not have an 8-bit word length, the
McBSP assumes the word length is eight bits, and LSB-first ordering is done.
DRR1
To CPU or DMA controller
DXR1
From CPU or DMA controller
SPRU592E