Make GSYNC = 1 when you want the McBSP and an external device to divide down the input clock with the
same phase relationship. If GSYNC = 1:
• An inactive-to-active transition on the FSR pin triggers a resynchronization of CLKG and a pulsing of FSG.
• CLKG always begins with a high state after synchronization.
• FSR is always detected at the same edge of the input clock signal that generates CLKG, no matter how long
the FSR pulse is.
• The FPER bits of SRGR2 are ignored because the frame-synchronization period on FSG is determined by
the arrival of the next frame-synchronization pulse on the FSR pin.
If GSYNC = 0, CLKG runs freely and is not resynchronized, and the frame-synchronization period on FSG is
determined by FPER.
15.3.3.1 Operating the Transmitter Synchronously with the Receiver
When GSYNC = 1, the transmitter can operate synchronously with the receiver, provided that:
• FSX is programmed to be driven by FSG (FSGM = 1 in SRGR2 and FSXM = 1 in PCR). If the input FSR has
appropriate timing so that it can be sampled by the falling edge of CLKG, it can be used, instead, by setting
FSXM = 0 and connecting FSR to FSX externally.
• The sample rate generator clock drives the transmit and receive clocking (CLKRM = CLKXM = 1 in PCR).
15.3.3.2 Synchronization Examples
show the clock and frame-synchronization operation with various polarities of
CLKR and FSR. These figures assume FWID = 0 in SRGR1, for an FSG pulse that is one CLKG cycle wide. The
FPER bits of SRGR2 are not programmed; the period from the start of a frame-synchronization 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).
FSG
(Needs resynchronization)
CLKG
resynchronize)
(No need to
CLKG
(FSRP=1)
FSR external
(FSRP=0)
FSR external
CLKR
CLKR
Figure 15-19. CLKG Synchronization and FSG Generation When GSYNC = 1 and CLKGDV = 1
Multichannel Buffered Serial Port (McBSP)
894
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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