D(R/X)
FS(R/X)
C5
C6
C7
B0
B2
B3
B4
B5
B6
B7
A0
A1
B1
CLK(R/X)
Preliminary
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Architecture
11.2.1.3.1 Clocking
Data is shifted one bit at a time from the McBSP.DR pin to the receive shift registers or from the
transmit shift registers to the McBSP.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) controls bit transfers from the McBSP.DR pin to the receive shift
registers. The transmit clock signal (CLKX) controls bit transfers from the transmit shift registers to the
McBSP.DX pin. CLKR or CLKX can be derived from a pin at the boundary of the McBSP
(McBSP.CLKR and McBSP.CLKX respectively) or derived from inside the McBSP. The polarities of
CLKR and CLKX are programmable.
gives an example in which the clock signal controls the timing of each bit transfer on the
pin.
Figure 11-3. Clock Signal Control of Bit Transfer Timing
The McBSP is constrained to operate at an internal functional frequency up to 55 MHz while CPU
interface (OCP compliant interface) can operate at a frequency up to 110 MHz. When driving CLKX or
CLKR at the pin, choose an appropriate input clock frequency. When using the internal sample rate
generator for CLKX/CLKR/CLKS, choose an appropriate input clock frequency (up to 110 MHz) and
divide down value (CLKDV).
11.2.1.3.2 Serial Words
Bits traveling between a shift register (RSR or XSR) and a data pin (McBSP.DR or McBSP.DX) are
transferred in a group called a serial word. You can define how many bits are in a word.
Bits coming in on the McBSP.DR pin are held in RSR until RSR holds a full serial word. Only then is
the word passed to the receive buffer RB (and ultimately to the DRR_REG register).
During transmission, XSR accept new data from transmit buffer XB after a full serial word has been
passed from XSR to the McBSP.DX pin.
In the example in
, an 8–bit word size was defined (see bits 7 through 0 of word B being
transferred).
11.2.1.3.3 Frames and Frame Synchronization
One or more words are transferred in a group called a frame. You can define how many words are in a
frame. All of the words in a frame are sent in a continuous stream. However, there can be pauses
between frame transfers. The McBSP uses frame–synchronization signals to determine when each
frame is received/transmitted. When a pulse occurs on a frame–synchronization signal, the McBSP
begins receiving/transmitting a frame of data. When the next pulse occurs, the McBSP
receives/transmits the next frame, and so on. Pulses on the receive frame–synchronization (FSR)
signal initiate frame transfers on McBSP.DR. Pulses on the transmit frame–sync (FSX) signal initiate
frame transfers on McBSP.DX. FSR or FSX can be derived from a pin at the boundary of the McBSP
(McBSP.FSR and McBSP.FSX respectively) or derived from inside the McBSP. In the example in
Figure 3, a one–word frame is transferred when a frame–synchronization pulse occurs. In McBSP
operation, the inactive–to–active transition of the frame–synchronization signal indicates the start of the
next frame. For this reason, the frame–synchronization signal may be high for an arbitrary number of
clock cycles. Only after the signal is recognized to have gone inactive, and then active again, does the
next frame synchronization occurs.
1127
SPRUGX9 – 15 April 2011
Multichannel Buffered Serial Port (McBSP)
© 2011, Texas Instruments Incorporated
Содержание TMS320C6A816 Series
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