Transmit Shift
Register
(XSR)
DXR
From CPU/DMA
Transmit Buffer
(XB)
REVERSE
(LSB first)
DX
Write of DXR (D)
D6
D7
B0
B1
B2
B3
B4
B5
B6
A1
Write of DXR (E)
DXR-to-XSR copy (D)
Write of DXR (C)
XRDY
DX
FSX
B7
A0
CLKX
DXR-to-XSR copy (B)
Preliminary
Architecture
www.ti.com
11.2.1.6 McBSP Transmission
This section explains the fundamental process of transmission in the McBSP.
and
show how transmission occurs in the McBSP.
shows the physical path for the data.
is a timing diagram showing signal
activity for one possible transmission scenario. A description of the process follows the figures.
Figure 11-9. McBSP Transmission Physical Data Path
Figure 11-10. McBSP Transmission Signal Activity
The following process shows how......
1. The CPU or the DMA controller writes data to the data transmit register. When the transmit buffer is
reached the transmitter ready bit (XRDY) is cleared in SPCR2_REG[1] register to indicate that the
transmitter is not ready for new data.
2. When new data arrives in DXR_REG register, the McBSP copies the content of the data transmit
register to the transmit buffer. In addition, th e Transmit Ready bit (XRDY) is set as long as the
buffer contains at least the transmit threshold number of free locations. This indicates that the
transmitter is ready to accept new data from the CPU or the DMA controller.
3. The McBSP waits for a transmit frame–synchronization pulse on internal FSX.
4. When the pulse arrives, the McBSP inserts the appropriate data delay that is selected with the
XCR2_REG[1:0] register XDATDLY bits. In the preceding timing diagram, a 1-bit data delay is
selected.
5. The McBSP shifts data bits from the transmit shift register to the McBSP.DX pin.
When activity is not properly timed, errors can occur. See the following topics for more details:
•
Underflow in the transmitter
•
Overflow in the transmitter
•
Unexpected transmit frame-synchronization pulse
1132
Multichannel Buffered Serial Port (McBSP)
SPRUGX9 – 15 April 2011
© 2011, Texas Instruments Incorporated
Содержание TMS320C6A816 Series
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