Architecture
1200
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Multichannel Buffered Serial Port (McBSP)
Example 25-1. CLKGDV = 0
CLKGDV = 0
S
G
= ( 1) × S
IN
= (0 + 1) × S
IN
= S
IN
Pulse width high = S
IN
× ( 1)/2 = S
IN
× (0+ 1)/2 = 0.5 × S
IN
Pulse width low = S
IN
× ( 1)/2 = S
IN
× (0+ 1)/2 = 0.5 × S
IN
Example 25-2. CLKGDV = 1
CLKGDV = 1
S
G
= ( 1) × S
IN
= (1 + 1) × S
IN
= 2 × S
IN
Pulse width high = S
IN
× ( 1)/2 = S
IN
× (1 +1)/2 = S
IN
Pulse width low = S
IN
× ( 1)/2 = S
IN
× (1+ 1)/2 = S
IN
Example 25-3. CLKGDV = 2
CLKGDV = 2
S
G
= ( 1) × S
IN
= (2 + 1) × S
IN
= 3 × S
IN
Pulse width high = S
IN
× (CLKGDV/2 + 1) = S
IN
× (2/2 + 1) = 2 × S
IN
Pulse width low = S
IN
× CLKGDV/2 = S
IN
× 2/2 = 1 × S
IN
25.2.5.3.3 Bit Clock Polarity: CLKSP
The external clock (CLKS) is selected to drive the sample rate generator clock divider by selecting
CLKSM = 0 in the sample rate generator register (SRGR) and SCLKME = 0 in the pin control register
(PCR). In this case, the CLKSP bit in SRGR selects the edge of CLKS on which sample rate generator
data bit clock (CLKG) and frame sync signal (FSG) are generated. Since the rising edge of CLKSRG
generates CLKG and FSG, the rising edge of CLKS when CLKSP = 0 or the falling edge of CLKS when
CLKSP = 1 causes the transition on CLKG and FSG.
25.2.5.3.4 Bit Clock and Frame Synchronization
When the external clock (CLKS) is selected to drive the sample rate generator (CLKSM = 0 in SRGR and
SCLKME = 0 in PCR), the GSYNC bit in SRGR can be used to configure the timing of CLKG relative to
CLKS. GSYNC = 1 ensures that the McBSP and the external device to which it is communicating are
dividing down the CLKS with the same phase relationship. If GSYNC = 0, this feature is disabled and
CLKG runs freely and is not resynchronized. If GSYNC = 1, an inactive-to-active transition on FSR triggers
a resynchronization of CLKG and the generation of FSG. CLKG always begins at a high state after
synchronization. Also, FSR is always detected at the same edge of CLKS that generates CLKG,
regardless of the length the FSR pulse. Although an external FSR is provided, FSG can still drive internal
receive frame synchronization when GSYNC = 1. When GSYNC = 1, FPER does not matter, because the
frame period is determined by the arrival of the external frame sync pulse.
and
show this operation with various polarities of CLKS and FSR. These figures
assume that FWID is 0, for a FSG = 1 CLKG wide.
These figures show what happens to CLKG when it is initially in sync and GSYNC = 1, as well as when it
is not in sync with the frame synchronization and GSYNC = 1.