SPRUJ17H March 2022 – October 2024 AM2631 , AM2631-Q1 , AM2632 , AM2632-Q1 , AM2634 , AM2634-Q1
By default, the clock division ratio is defined by the MCSPI_CHCONF_0/1/2/3[5-2] CLKD bit field with power-of-2 granularity leading to a clock division in the range 1 to 4096; in this case, the duty cycle is always 50 percent. With the MCSPI_CHCONF_0/1/2/3[29] CLKG bit, clock division granularity can be changed to one clock cycle; in that case the MCSPI_CHCTRL_0/1/2/3[15-8] EXTCLK bit field is concatenated with the MCSPI_CHCONF_0/1/2/3[5-2] CLKD bit field to give a 12-bit-wide division ratio in the range 1 to 4096.
When granularity is one clock cycle (the CLKG bit set to 1), for the odd value of the clock ratio, the clock high level lasts one clock cycle more than the low level, depending on the MCSPI_CHCONF_0/1/2/3[1] POL and MCSPI_CHCONF_0/1/2/3[0] PHA bits (see Table 13-28).
Clock Ratio FRATIO | CLKSPIO High Time | CLKSPIO Low Time |
---|---|---|
1 | THIGH_REF | TLOW_REF |
Even >= 2 | T_ref * (FRATIO/2) | T_ref * (FRATIO/2) |
Odd >= (POL = PHA) | T_ref * (FRATIO– 1)/2 | T_ref * (FRATIO + 1)/2 |
Odd >= (POL =! PHA) | T_ref * (FRATIO+ 1)/2 | T_ref * (FRATIO – 1)/2 |
FRATIO = SPICLK
frequency (FOUT) division ratio
THIGH = SPICLK high time period
TLOW = SPICLK low time period
T_ref
= MCSPI_FCLK period
THIGH_REF =
MCSPI_FCLK high time period
TLOW_REF =
MCSPI_FCLK low time period
If the CLKG bit is set to 1; FRATIO = EXTCLK concatenated with CLKD + 1.
For odd ratio values, the duty cycle is calculated as follows:
Duty_cycle = (1 – 1/FRATIO)/2
Table 13-29 shows examples of clock granularity with a clock source frequency of 50 MHz.
EXTCLK | CLKD | CLKG | FRATIO | PHA | POL | THIGH (ns) | TLOW (ns) | TPERIOD (ns) | Duty Cycle | FOUT (MHz) |
---|---|---|---|---|---|---|---|---|---|---|
X | 0 | 0 | 1 | X | X | 10.0 | 10.0 | 20.0 | 50–50 | 50 |
X | 1 | 0 | 2 | X | X | 20.0 | 20.0 | 40.0 | 50–50 | 25 |
X | 2 | 0 | 4 | X | X | 40.0 | 40.0 | 80.0 | 50–50 | 12.5 |
X | 3 | 0 | 8 | X | X | 80.0 | 80.0 | 160.0 | 50–50 | 6.2 |
0 | 0 | 1 | 1 | X | X | 10.0 | 10.0 | 20.0 | 50–50 | 50 |
0 | 1 | 1 | 2 | X | X | 20.0 | 20.0 | 40.0 | 50–50 | 25 |
0 | 2 | 1 | 3 | 1 | 0 | 40.0 | 20.0 | 60.0 | 66–33 | 16.6 |
0 | 2 | 1 | 3 | 1 | 1 | 20.0 | 40.0 | 60.0 | 33–66 | 16.6 |
0 | 3 | 1 | 4 | X | X | 40.0 | 40.0 | 80.0 | 50–50 | 12.5 |
5 | 0 | 1 | 81 | 1 | 0 | 820.0 | 800.0 | 1620.0 | 50.6–49.4 | 0.617 |
5 | 7 | 1 | 88 | X | X | 880.0 | 880.0 | 1760.0 | 50–50 | 0.568 |