SPRUJ53B April 2024 – September 2024 TMS320F28P550SJ , TMS320F28P559SJ-Q1
The following diagrams show the ADC conversion timings for two SOCs given the following assumptions:
Table 15-8 describes the parameters in the following timing diagrams. .
Table 15-9 and Table 15-10 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 or trigger the DMA 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). | |
tDMA | The time from the end of the S+H window until a DMA read of the ADC conversion result is triggered, when ADCCTL1.TDMAEN = 1. |
If TDMAEN is set to 0, then the DMA trigger occurs at TINT. In certain conditions, the ADCINT flag can be set before the ADCRESULT value is latched. To make sure that the DMA read occurs after the ADCRESULT value has been latched, write 1 to ADCCTL1.TDMAEN to enable DMA timings. |
ADCCLK Prescale | SYSCLK Cycles | |||||
---|---|---|---|---|---|---|
ADCCTL2. PRESCALE | Prescale Ratio | tEOC | tLAT | tINT
(Early)(1) |
tINT (Late) |
tDMA |
0 | 1 | 15 | 20 | 1 | 15 | 20 |
2 | 2 | 30 | 35 | 1 | 30 | 35 |
3 | 2.5 | 38 | 46 | 1 | 38 | 46 |
4 | 3 | 45 | 50 | 1 | 45 | 50 |
5 | 3.5 | 53 | 58 | 1 | 53 | 58 |
6 | 4 | 60 | 65 | 1 | 60 | 65 |
7 | 4.5 | 68 | 73 | 1 | 68 | 73 |
8 | 5 | 75 | 80 | 1 | 75 | 80 |
9 | 5.5 | 83 | 88 | 1 | 83 | 88 |
10 | 6 | 90 | 95 | 1 | 90 | 95 |
11 | 6.5 | 98 | 103 | 1 | 98 | 103 |
12 | 7 | 105 | 110 | 1 | 105 | 110 |
13 | 7.5 | 113 | 118 | 1 | 113 | 118 |
14 | 8 | 120 | 125 | 1 | 120 | 125 |
15 | 8.5 | 128 | 133 | 1 | 128 | 133 |
ADCCLK Prescale | SYSCLK Cycles | |||||
---|---|---|---|---|---|---|
ADCCTL2. PRESCALE | Prescale Ratio | tEOC | tLAT | tINT
(Early)(1) |
tINT (Late) |
tDMA |
0 | 1 | 14 | 19 | 1 | 14 | 19 |
2 | 2 | 28 | 33 | 1 | 28 | 33 |
3 | 2.5 | 35 | 40 | 1 | 35 | 40 |
4 | 3 | 42 | 47 | 1 | 42 | 47 |
5 | 3.5 | 49 | 54 | 1 | 49 | 54 |
6 | 4 | 56 | 61 | 1 | 56 | 61 |
7 | 4.5 | 63 | 68 | 1 | 63 | 68 |
8 | 5 | 70 | 75 | 1 | 70 | 75 |
9 | 5.5 | 77 | 82 | 1 | 77 | 82 |
10 | 6 | 84 | 89 | 1 | 84 | 89 |
11 | 6.5 | 91 | 96 | 1 | 91 | 96 |
12 | 7 | 98 | 103 | 1 | 98 | 103 |
13 | 7.5 | 105 | 110 | 1 | 105 | 110 |
14 | 8 | 112 | 117 | 1 | 112 | 117 |
15 | 8.5 | 119 | 124 | 1 | 119 | 124 |