Table 15-5. Choosing an Input Clock for the Sample Rate Generator with the
SCLKME and CLKSM Bits
SCLKME
CLKSM
Input Clock for Sample Rate Generator
0
0
Reserved
0
1
LSPCLK
1
0
Signal on MCLKR pin
1
1
Signal on MCLKX pin
15.3.1.3 Choosing a Polarity for the Input Clock
, when the input clock is received from a pin, you can choose the polarity of the input
clock. The rising edge of CLKSRG generates CLKG and FSG, but you can determine which edge of the input
clock causes a rising edge on CLKSRG. The polarity options and their effects are described in
CLKSRG
0
1
CLKXP
MCLKX pin
CLKRP
MCLKR pin
0
1
LSPCLK
CLKSM
0
1
SCLKME
To clock dividers
Reserved
Figure 15-18. Possible Inputs to the Sample Rate Generator and the Polarity Bits
Table 15-6. Polarity Options for the Input to the Sample Rate Generator
Input Clock
Polarity Option
Effect
LSPCLK
Always positive polarity
Rising edge of CPU clock generates transitions on CLKG and FSG.
Signal on MCLKR pin
CLKRP = 0 in PCR
Falling edge on MCLKR pin generates transitions on CLKG and FSG.
CLKRP = 1 in PCR
Rising edge on MCLKR pin generates transitions on CLKG and FSG.
Signal on MCLKX pin
CLKXP = 0 in PCR
Rising edge on MCLKX pin generates transitions on CLKG and FSG.
CLKXP = 1 in PCR
Falling edge on MCLKX pin generates transitions on CLKG and FSG.
15.3.1.4 Choosing a Frequency for the Output Clock (CLKG)
The input clock (LSPCLK or external clock) can be divided down by a programmable value to drive CLKG.
Regardless of the source to the sample rate generator, the rising edge of CLKSRG (see
) generates
CLKG and FSG.
The first divider stage of the sample rate generator creates the output clock from the input clock. This divider
stage uses a counter that is preloaded with the divide down value in the CLKGDV bits of SRGR1. The output of
this stage is the data clock (CLKG). CLKG has the frequency represented by
.
CLKG frequency
+
Input clock frequency
(CLKGDV
)
1)
(12)
Thus, the input clock frequency is divided by a value between 1 and 256. When CLKGDV is odd or equal to
0, the CLKG duty cycle is 50%. When CLKGDV is an even value, 2p, representing an odd divide down, the
high-state duration is p+1 cycles and the low-state duration is p cycles.
Multichannel Buffered Serial Port (McBSP)
892
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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