SPRUHM9H October 2014 – May 2024 TMS320F28075 , TMS320F28075-Q1 , TMS320F28076
The following diagrams show the ADC conversion timings for two SOCs given the following assumptions:
Table 10-8 describes the parameters in the following timing diagrams. Table 10-9 lists the ADC timings..
Parameter | Description |
---|---|
tSH | The duration of the S+H window. |
At the end of this window, the value on the S+H capacitor becomes the voltage to be converted into a digital value. The duration is given by (ACQPS + 1) SYSCLK cycles. ACQPS can be configured individually for each SOC, so tSH is not necessarily the same for different SOCs. | |
Note: The value on the S+H capacitor is captured approximately 5ns before the end of the S+H window regardless of device clock settings. | |
tLAT | The time from the end of the S+H window until the ADC results latch in the ADCRESULTx register. |
If the ADCRESULTx register is read before this time, the previous conversion results are returned. | |
tEOC | The time from the end of the S+H window until the S+H window for the next ADC conversion can begin. The subsequent sample can start before the conversion results are latched. |
tINT | The time from the end of the S+H window until an ADCINT flag is set (if configured). |
If the INTPULSEPOS bit in the ADCCTL1 register is set, tINT coincides with the end of conversion (EOC) signal. | |
If the INTPULSEPOS bit is 0, and the OFFSET field in the ADCINTCYCLE register is not 0, then there is a delay of OFFSET SYSCLK cycles before the ADCINT flag is set. This delay can be used to enter the ISR exactly when the sample is ready. | |
If the INTPULSEPOS bit is 0, tINT coincides with the end of the S+H window. If tINT triggers a read of the ADC result register (directly through DMA or indirectly by triggering an ISR that reads the result), care must be taken to make sure the read occurs after the results latch (otherwise, the previous results are read). |
ADCCLK Prescale | SYSCLK Cycles | ||||
---|---|---|---|---|---|
ADCCTL2. PRESCALE | Prescale Ratio | tEOC | tLAT(1) | tINT
(Early)(2) |
tINT (Late) |
0 | 1 | 11 | 13 | 0 | 11 |
2 | 2 | 21 | 23 | 0 | 21 |
3 | 2.5 | 26 | 28 | 0 | 26 |
4 | 3 | 31 | 34 | 0 | 31 |
5 | 3.5 | 36 | 39 | 0 | 36 |
6 | 4 | 41 | 44 | 0 | 41 |
7 | 4.5 | 46 | 49 | 0 | 46 |
8 | 5 | 51 | 55 | 0 | 51 |
9 | 5.5 | 56 | 60 | 0 | 56 |
10 | 6 | 61 | 65 | 0 | 61 |
11 | 6.5 | 66 | 70 | 0 | 66 |
12 | 7 | 71 | 76 | 0 | 71 |
13 | 7.5 | 76 | 81 | 0 | 76 |
14 | 8 | 81 | 86 | 0 | 81 |
15 | 8.5 | 86 | 91 | 0 | 86 |