Preliminary
Architecture
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Frame-synchronization pulse-width countdown. CLKG cycles are counted according to the
SRGR1_REG[15:8] register FWID bits to control the width of each frame-synchronization pulse.
Note: The McBSP cannot operate at an internal functional frequency faster than 55 MHz. Choose an
input clock frequency and a CLKDV value such that CLKG is less than or equal to 55 MHz.
In addition to the three-stage clock divider, the sample rate generator has a frame-synchronization
pulse detection and clock synchronization module that allows synchronization of the clock divide down
with an incoming frame-synchronization pulse on the McBSP.FSR pin. This feature is enabled or
disabled with the SRGR2_REG[15] register GSYNC bit.
CLKG is used as source in order to generate the output clocks CLKX/CLKR when the CLKXM/CLKRM
indicates that the clock is an output. The output CLKX/CLKR is generated according to the clock
polarity setting given by the CLKXP/CLKRP as follows: when falling edge, the CLKX/CLKR is CLKG
inverted.
11.2.2.1 Clock Generation in the Sample Rate Generator
The sample rate generator can produce a clock signal (CLKG) for use by the receiver, the transmitter,
or both. Use of the sample rate generator to drive clocking is controlled by the clock mode bits (CLKRM
and CLKXM) in the pin control register (PCR_REG[8] and PCR_REG[9] respectively) and polarity mode
bits (CLKRP and CLKXP).
When a clock mode bit is set to 1 (CLKRM = 1 for reception, CLKXM = 1 for transmission), the
corresponding data clock (CLKR for reception, CLKX for transmission) is driven by the internal sample
rate generator output clock (CLKG) according with the polarity setting.
The effects of CLKRM = 1 and CLKXM = 1 on the McBSP are partially affected by the use of the digital
loop back mode, the analog loop back mode and by the synchronous receive/transmit setting,
respectively, as described in
. The analog loop back mode is selected with the
SPCR1_REG[15] register ALB bit. The digital loop back mode is selected with the DLB bit of the
XCCR_REG register. The synchronous mode is controlled by the ALBRXCTRL input pin.
When using the sample rate generator as a clock source, make sure the sample rate generator is
enabled (GRST = 1).
Table 11-2. Effects of DLB and ALB Bits on Clock Modes
Mode Bit Settings
Effect
CLKRM = 1
DLB = 0 & ALB = 0
CLKR is an output pin driven by the sample rate generator
(Digital & analog loop back mode
output clock (CLKG).
disabled)
DLB = 0 & ALB = 1
CLKR is an output pin driven by the sample rate generator
(Analog loop back mode enabled)
output clock (CLKG).
The receive functional part internal clock is driven by CLKX input
pin CLKXI. The source of CLKX depends on the CLKXM bit.
The receive frame synchronization is driven by FSX input pin
(FSXI).
The receive data is driven by the DX loop back pin (DXI).
DLB = 1 & ALB = 0
CLKR is not driven.
(Digital loop back mode enabled)
The sample rate generator and the frame synchronization
generator need to be enabled.
The internal transmit and receive clocks are driven by SRG
(CLKG having the appropriate CLKXP polarity).
The transmit and receive frame synchronization signals are
driven by FSG (having the appropriate FSXP polarity).
The transmit data is connected to the receive input data.
Note that in digital loop back mode no serial link activity will be
seen by the remote device because CLKREN, CLKXEN,
FSREN, FSRXEN, DXEN are not active.
DLB = 1 & ALB = 1 (reserved mode)
Undefined functionality.
1134Multichannel Buffered Serial Port (McBSP)
SPRUGX9 – 15 April 2011
© 2011, Texas Instruments Incorporated
Содержание TMS320C6A816 Series
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