I am looking at the technical reference manual for TMS320F28004x Piccolo Microcontrollers (Literature Number: SPRUI33A).
Referring to 13.3.1 Ensuring Synchronous Operation, which states "For best performance, all ADCs on the device should be operated synchronously. The device datasheet specifies the performance in both synchronous and asynchronous mode for those parameters which differ between the modes of operation."
1. Referring to the datasheet for "TMS320F28004x Piccolo™ Microcontrollers," Table 5-43. ADC Characteristics, Parameter "ADC-to-ADC Isolation" and "ENOB" show "Not Supported" for Asynchronous ADCs. So it would seem to me that this isn't really a suggestion, but rather a requirement as operating in this mode is undefined. Please confirm.
2. So I can better understand what is going on, can you please explain further why asynchronous mode is not supported, why the hardware as this limitation. The datasheet says "Each ADC module consists of a single sample-and-hold (S/H) circuit. The ADC module is designed to be duplicated multiple times on the same chip, allowing simultaneous sampling or independent operation of multiple ADCs." This lead me to believe I could just use each module however I see fit. Instead it seems I must pay very careful attention to how they are operated with respect to one another.
3. Lastly, just to confirm my understanding with a example application. Let's say ADC-A is operating SOC0-SOC3 at a predetermined interval for SMPS control. ADC-B SOC0 is triggered asynchronously, by an external device flagging an interrupt that a voltage needs to be sampled immediately. Therefore it is possible ADC-B SOC0 can be triggered to overlap ADC-A SOC1-3 and violate the Synchronous Operation requirement. The workaround that comes to mind would be, in the interrupt, to schedule the ADC-B SOC0 to synchronize with ADC-A SOC0, but this would potentially add a delay and defeat the purpose of using the interrupt in the first place. Am I understanding this correctly? This limits ADC operation but I don't want inaccurate results.
Thank you very much!