Setting the Transmit Frame-Sync Mode
8-23
Transmitter Configuration
SPRU592E
18 also shows the effect of each bit setting on the FSX pin. The
polarity of the signal on the FSX pin is determined by the FSXP bit.
Table 8
−
18. How FSXM and FSGM Select the Source of Transmit Frame-Sync Pulses
FSXM
FSGM
Source of Transmit Frame
Synchronization
FSX Pin Status
0
0 or 1
An external frame-sync signal enters the
McBSP through the FSX pin. The signal is
then inverted by FSXP before being used
as internal FSX.
Input
1
1
Internal FSX is driven by the sample rate
generator frame-sync signal (FSG).
Output. FSG is inverted by FSXP before
being driven out on FSX pin.
1
0
A DXR-to-XSR copy causes the McBSP to
generate a transmit frame-sync pulse that
is 1 cycle wide.
Output. The generated frame-sync pulse is
inverted as determined by FSXP before
being driven out on FSX pin.
8.16.2 Other Considerations
If the sample rate generator creates a frame-sync signal (FSG) that is derived
from an external input clock, the GSYNC bit determines whether FSG is kept
synchronized with pulses on the FSR pin.
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 and must
provide a slave-enable signal (SS) on the FSX pin, make sure that FSXM = 1
and FSGM = 0, so that FSX is an output and is driven active for the duration
of each transmission. If the McBSP is a slave, make sure that FSXM = 0, so
that the McBSP can receive the slave-enable signal on the FSX pin.
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