15.8.18 Set the Transmit Clock Mode
Table 15-66. Register Bit Used to Set the Transmit Clock Mode
Register
Bit
Name
Function
Type
Reset
Value
PCR
9
CLKXM
Transmit clock mode
R/W
0
CLKXM = 0
The transmitter gets its clock signal from an external
source via the MCLKX pin.
CLKXM = 1
The MCLKX pin is an output pin driven by the
sample rate generator of the McBSP.
15.8.18.1 Selecting a Source for the Transmit Clock and a Data Direction for the MCLKX pin
shows how the CLKXM bit selects the transmit clock and the corresponding status of the MCLKX
pin. The polarity of the signal on the MCLKX pin is determined by the CLKXP bit.
Table 15-67. How the CLKXM Bit Selects the Transmit Clock and the Corresponding Status of the MCLKX
pin
CLKXM in
PCR
Source of Transmit Clock
MCLKX pin Status
0
Internal CLKX is driven by an external clock on the MCLKX pin.
CLKX is inverted as determined by CLKXP before being used.
Input
1
Internal CLKX is driven by the sample rate generator clock, CLKG. Output. CLKG, inverted as determined by CLKXP, is
driven out on CLKX.
15.8.18.2 Other Considerations
If the sample rate generator creates a clock signal (CLKG) that is derived from an external input clock, the
GSYNC bit determines whether CLKG is kept synchronized with pulses on the FSR pin. For more details, see
In the clock stop mode (CLKSTP = 10b or 11b), the McBSP can act as a master or as a slave in the SPI
protocol. If the McBSP is a master, make sure that CLKXM = 1 so that CLKX is an output to supply the master
clock to any slave devices. If the McBSP is a slave, make sure that CLKXM = 0 so that CLKX is an input to
accept the master clock signal.
15.8.19 Set the Transmit Clock Polarity
Table 15-68. Register Bit Used to Set Transmit Clock Polarity
Register
Bit
Name
Function
Type
Reset
Value
PCR
1
CLKXP
Transmit clock polarity
R/W
0
CLKXP = 0
Transmit data sampled on rising edge of CLKX.
CLKXP = 1
Transmit data sampled on falling edge of CLKX.
15.8.19.1 Frame Synchronization Pulses, Clock Signals, and Their Polarities
Transmit frame-synchronization pulses can be either generated internally by the sample rate generator
(see
) or driven by an external source. The source of frame synchronization is selected by
programming the mode bit, FSXM, in PCR. FSX is also affected by the FSGM bit in SRGR2. For information
about the effects of FSXM and FSGM, see
). Similarly, transmit clocks can be selected to be
inputs or outputs by programming the mode bit, CLKXM, in the PCR (see
When FSR and FSX are inputs (FSXM = FSRM= 0, external frame-synchronization pulses), the McBSP detects
them on the internal falling edge of clock, internal MCLKR, and internal CLKX, respectively. The receive data
arriving at the DR pin is also sampled on the falling edge of internal MCLKR. These internal clock signals are
either derived from external source via CLK(R/X) pins or driven by the sample rate generator clock (CLKG)
internal to the McBSP.
Multichannel Buffered Serial Port (McBSP)
952
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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