Sample rate
generator
CLKS
mcbspi _clkx
CLKXP bit
CLKSP bit
CLKXM bit
CLKXP bit
0
1
CLKXM bit
CLKX _int
Transmitter
XIOEN bit
mcbspi _clkr
CLKRP bit
CLKRM bit
CLKRP bit
0
1
CLKRM bit
CLKR _int
RIOEN bit
1
0
DLB bit
Receiver
CLKG
mcbspi _fsx
FSXP bit
FSXM bit
FSXP bit
0
1
FSXM bit
FSX_int
XIOEN bit
mcbspi _fsr
FSRP bit
FSRM bit and GSYNC bit
FSRP bit
0
1
FSRM bit
FSR_int
RIOEN bit
1
0
DLB bit
FSG
0
1
FSGM bit
Data transmission
between DXR to XSR
FSR_int
GSYNC bit
FWID bit
CLKGDV bit
FPER bit
CLKSM bit
McBSPi _ICLK
mcbsp _clk s
McBSPi_FCLK
mcbsp-025
Public Version
McBSP Functional Description
www.ti.com
21.4.2.2 Bit Reordering (Option to Transfer LSB First)
Generally, the McBSP module transmits or receives all data with the MSB first. However, some data
protocols require the LSB to be transferred first.
If you set McBSPi.
[4:3] XREVERSE=0b01, the bit ordering of the data words is
reversed (LSB first) before being sent to the serial port. If you set McBSPi.
RREVERSE=0b01, the bit ordering of the data words is reversed during reception (LSB first).
This feature is available for all the data formats from 8 up to 32-bit data length.
21.4.2.3 Clocking and Framing Data
This section explains basic concepts and terminology important for understanding how McBSP data
transfers are timed and delimited.
Figure 21-26. Conceptual Block Diagram for Clock and Frame Generation
21.4.2.3.1 Clocking
Data is shifted one bit at a time from the mcbspi_dr pin to the RSRs or from the XSRs to the mcbspi_dx
pin. The time for each bit transfer is controlled by the rising or falling edge of a clock signal.
The receive clock signal (CLKR_int) controls bit transfers from the mcbspi_dr pin to the RSRs. The
transmit clock signal (CLKX_int) controls bit transfers from the XSRs to the mcbspi_dx pin. CLKR_int or
CLKX_int signals can be derived from a pin at the boundary of the McBSP module (mcbspi_clkr and
mcbspi_clkx respectively) or derived from inside the McBSP module (see
). The clocks
source is selected by programming the McBSPi.
[9] CLKXM bit and the
McBSPi.
[8] CLKRM bit respectively.
When the McBSPi.
[9] CLKXM bit (transmitter clock mode) is set to:
•
‘0’, CLKX_int is driven by an external clock and mcbspi_clkx is an input pin.
•
‘1’, CLKX_int is driven by the internal sample rate generator and mcbspi_clkx is an output pin.
For the McBSPi.
[8] CLKRM bit (receiver clock mode), see
.
3094
Multi-Channel Buffered Serial Port
SWPU177N – December 2009 – Revised November 2010
Copyright © 2009–2010, Texas Instruments Incorporated