
Data Transfer Process of a McBSP
2-3
McBSP Operation
SPRU592E
2.1.2 Data Transfer Process for Word Length of 20, 24, or 32 Bits
If the word length is larger than 16 bits, two 16-bit registers are needed at each
stage of the data transfer paths. The registers DRR2, RBR2, RSR2, DXR2,
and XSR2 are needed to hold the most significant bits.
Receive data arrives on the DR pin and is shifted into RSR2 and RSR1. Once
the full word is received, the contents of RSR2 and RSR1 are copied to RBR2
and RBR1, respectively, only if RBR1 is not full. Then the contents of RBR2
and RBR1 are copied to DRR2 and DRR1, respectively, unless the previous
content of DRR1 has not been read by the CPU or the DMA controller. The
CPU or the DMA controller must read data from DRR2 first and then from
DRR1. When DRR1 is read, the next RBR-to-DRR copy occurs.
For reception, the RJUST field in register SPCR1 controls the way the received
data is aligned in DRR2 and DRR1. For transmission, the CPU or the DMA
controller must write data to DXR2 first and then to DXR1. When new data
arrives in DXR1, if there is no previous data in XSR1, the contents of DXR2
and DXR1 are copied to XSR2 and XSR1, respectively; otherwise, the
contents of the DXRs are copied to the XSRs when the last bit of the previous
data is shifted out on the DX pin. After transmit frame synchronization, the
transmitter begins shifting bits from the XSRs to the DX pin.
Содержание TMS320VC5509
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