McBSP Registers
1139
SPRUH22I – April 2012 – Revised November 2019
Copyright © 2012–2019, Texas Instruments Incorporated
C28 Multichannel Buffered Serial Port (McBSP)
Table 15-86. Pin Control Register (PCR) Field Descriptions (continued)
Bit
Field
Value
Description
9
CLKXM
Transmit clock mode bit. CLKXM determines whether the source for the transmit clock is
external or internal, and whether the MCLKX pin is an input or an output. The polarity of the
signal on the MCLKX pin is determined by the CLKXP bit.
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 CLKX is an output. If the McBSP
is a slave, make sure that CLKX is an input.
Not in clock stop mode (CLKSTP = 00b or 01b):
0
The transmitter gets its clock signal from an external source via the MCLKX pin.
1
Internal CLKX is driven by the sample rate generator of the McBSP. The MCLKX pin is an
output pin that reflects internal CLKX.
In clock stop mode (CLKSTP = 10b or 11b):
0
The McBSP is a slave in the SPI protocol. The internal transmit clock (CLKX) is driven by the
SPI master via the MCLKX pin. The internal receive clock (MCLKR) is driven internally by
CLKX, so that both the transmitter and the receiver are controlled by the external master clock.
1
The McBSP is a master in the SPI protocol. The sample rate generator drives the internal
transmit clock (CLKX). Internal CLKX is reflected on the MCLKX pin to drive the shift clock of
the SPI-compliant slaves in the system. Internal CLKX also drives the internal receive clock
(MCLKR), so that both the transmitter and the receiver are controlled by the internal master
clock.
8
CLKRM
Receive clock mode bit. The role of CLKRM and the resulting effect on the MCLKR pin depend
on whether the McBSP is in the digital loopback mode (DLB = 1).
The polarity of the signal on the MCLKR pin is determined by the CLKRP bit.
Not in digital loopback mode (DLB = 0):
0
The MCLKR pin is an input pin that supplies the internal receive clock (MCLKR).
1
Internal MCLKR is driven by the sample rate generator of the McBSP. The MCLKR pin is an
output pin that reflects internal MCLKR.
In digital loopback mode (DLB = 1):
0
The MCLKR pin is in the high impedance state. The internal receive clock (MCLKR) is driven
by the internal transmit clock (CLKX). CLKX is derived according to the CLKXM bit.
1
Internal MCLKR is driven by internal CLKX. The MCLKR pin is an output pin that reflects
internal MCLKR. CLKX is derived according to the CLKXM bit.
7
SCLKME
Sample rate generator input clock mode bit. The sample rate generator can produce a clock
signal, CLKG. The frequency of CLKG is:
CLKG freq. = (Input clock frequency) / ( 1)
SCLKME is used in conjunction with the CLKSM bit to select the input clock.
SCLKME
CLKSM
Input Clock For
Sample Rate Generator
0
0
Reserved
0
1
LSPCLK
The input clock for the sample rate generator is taken from the MCLKR pin or from the MCLKX
pin, depending on the value of the CLKSM bit of SRGR2:
SCLKME
CLKSM
Input Clock For
Sample Rate Generator
1
0
Signal on MCLKR pin
1
1
Signal on MCLKX pin
6-4
Reserved
Reserved
3
FSXP
Transmit frame-synchronization polarity bit. FSXP determines the polarity of FSX as seen on
the FSX pin.
0
Transmit frame-synchronization pulses are active high.
1
Transmit frame-synchronization pulses are active low.
2
FSRP
Receive frame-synchronization polarity bit. FSRP determines the polarity of FSR as seen on
the FSR pin.
0
Receive frame-synchronization pulses are active high.
1
Receive frame-synchronization pulses are active low.