CLKG
FSG
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
Frame-
CLKG
×
sync pulse width: (FWID + 1)
Frame-sync period: (FPER + 1)
CLKG
×
Preliminary
Architecture
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11.2.8.5.17 Set the SRG Frame-Sync Period and Pulse Width
FPER bit field (SRGR2_REG[11:0]) is used to set the SRG frame-sync period and FWID bit field
(SRGR1_REG[15:8]) is used to set the SRG pulse width. The sample rate generator can produce a
clock signal, CLKG, and a frame–synchronization signal, FSG. If the sample rate generator is supplying
receive or transmit frame synchronization, you must program the bit fields FPER and FWID.
On FSG, the period from the start of a frame–synchronization pulse to the start of the next pulse is
(FPER + 1) CLKG cycles. The 12 bits of FPER allow a frame–synchronization period of 1 to 4096
CLKG cycles, which allows up to 4096 data bits per frame. When GSYNC = 1, FPER is a don’t care
value.
Each pulse on FSG has a width of (FWID + 1) CLKG cycles. The eight bits of FWID allow a pulse width
of 1 to 256 CLKG cycles. It is recommended that FWID be programmed to a value less than the
programmed word length.
The values in FPER and FWID are loaded into separate down–counters. The 12–bit FPER counter
counts down the generated clock cycles from the programmed value (4095 maximum) to 0. The 8–bit
FWID counter counts down from the programmed value (255 maximum) to 0.
shows a frame–synchronization period of 16 CLKG periods (FPER = 15 or 0000 1111b)
and a frame–synchronization pulse with an active width of 2 CLKG periods (FWID = 1).
When the sample rate generator comes out of reset, FSG is in its inactive state. Then, when GRST = 1
and FSGM = 1, a frame–synchronization pulse is generated. The frame width value (FWID + 1) is
counted down on every CLKG cycle until it reaches 0, at which time FSG goes low. At the same time,
the frame period value (FPER + 1) is also counting down. When this value reaches 0, FSG goes high,
indicating a new frame.
Figure 11-29. Frame of 16 CLKG Periods and Active Width of 2 CLKG Periods
11.2.8.5.18 Set the Receive Clock Mode
CLKRM bit (PCR_REG[8]), ALB bit (SPCR1_REG[15]) and DLB bit field (XCCR_REG) are used to set
the receive clock mode.
shows how you can select various sources to provide the receive clock signal and affect
the McBSP.CLKR pin. The CLKRP bit determines the polarity of the signal on the McBSP.CLKR pin.
In the digital loop-back mode (DLB = 1) or analog loop-back mode (ALB = 1), the transmit clock signal
is used as the receive clock signal.
Table 11-14. CLKRM Effect on Receive Clock Signal and McBSP.CLKR Pin
CLKRM
Source of Receive Clock
McBSP.CLKR Pin Status
0
The McBSP.CLKR pin is an input driven by an external clock.
Input
The external clock signal is inverted as determined by CLKRP
before being used.
1
The sample rate generator clock (CLKG) drives internal CLKR.
Output. CLKG, inverted as determined by
CLKRP, is driven out on the McBSP.CLKR pin.
1164Multichannel Buffered Serial Port (McBSP)
SPRUGX9 – 15 April 2011
© 2011, Texas Instruments Incorporated
Содержание TMS320C6A816 Series
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