Synchronizing Sample Rate Generator Outputs to an External Clock
Sample Rate Generator of the McBSP
3-10
SPRU592E
3.4 Synchronizing Sample Rate Generator Outputs to an External Clock
The sample rate generator can produce a clock signal (CLKG) and a
frame-sync signal (FSG) based on an input clock signal that is either the
McBSP internal input clock signal or a signal at the CLKS or CLKR pin. When
an external clock is selected to drive the sample rate generator, the GSYNC
bit of SRGR2 and the FSR pin can be used to control the timing of CLKG and
the pulsing of FSG relative to the chosen input clock.
Make GSYNC = 1 when you want the McBSP and an external device to be
synchronized with the same phase relationship. If GSYNC = 1:
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An inactive-to-active transition on the FSR pin triggers a
resynchronization of CLKG and a pulsing of FSG.
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CLKG always begins with a high state after synchronization.
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FSR is always detected at the same edge of the input clock signal that
generates CLKG, no matter how long the FSR pulse is.
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The FPER bits of SRGR2 are ignored because the frame-sync period on
FSG is determined by the arrival of the next frame-sync pulse on the FSR
pin.
If GSYNC = 0, CLKG runs freely and is not resynchronized, and the
frame-sync period on FSG is determined by FPER.
This clock synchronization is not supported on TMS320VC5501 and
TMS320VC5502 devices.
3.4.1 Synchronization Examples
4 show the clock and frame-synchronization
operation with various polarities of CLKS (the chosen input clock) and FSR.
These figures assume FWID = 0 in SRGR1, for an FSG pulse that is
1 CLKG cycle wide. The FPER bits of SRGR2 are not programmed; the period
from the start of a frame-sync pulse to the start of the next pulse is determined
by the arrival of the next inactive-to-active transition on the FSR pin. Each of
the figures shows what happens to CLKG when it is initially synchronized and
GSYNC = 1, and when it is not initially synchronized and GSYNC = 1. The
second figure has a slower CLKG frequency (it has a larger divide-down value
in the CLKGDV bits of SRGR1).
Summary of Contents for TMS320VC5509
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Page 191: ...General Purpose I O on the McBSP Pins 9 4 SPRU592E This page is intentionally left blank ...
Page 201: ...Emulation Power and Reset Considerations 10 10 SPRU592E ...
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