I am using F28335 and need to interface upto 24 external ADC channels from ADS8556 with the MCU ( these are additional channels beyond the inbuilt ADC). What is the best way to interface - SPI / McBSP?
Also, will I need to use an external channel multiplexer if using McBSP ?
A possibility might be to use the parallel interface mode. The TMS320F28335 supports an external memory interface called the XINTF. You need to have some logic to expand the addresses with the 3 chip selects available on the interface.
Actually I plan to have following interfaces on F28335 -
1. 16 channels using in-built ADCs
2. 24 external ADC channels
3. MCU - FPGA via EMIF/XINT
4. External SDRAM via EMIF/XINT
Given these interfaces, I think I will have to share the XINT address space for external RAM and FPGA connections; can ADC channels still be shared on same XINT ?
In this scenario, will McBSP be a better option ... want your suggestions on these interfaces
I don't see any reason why keeping the ADS8556 on the EMIF would be an issue. You'd have to address decode the /CS input (using something like an SN74HC138) and you could potentially use the SOC from the F28335 to trigger the CONVST inputs. I believe the McBSP is in the low-speed clock domain which might be problematic in your control loop if you used the serial mode of the ADS8556.
Thank you for your reply. I tried looking up some documentation and example code like adc_on_xintf and xintf_run_from. I'm not sure if I can use ADC channels, FPGA connection and SARAM simultaneously using same XINTF. Given a single data bus XD [31:0], even if I allocate something like ADC on Zone 0, FPGA on Zone 6 and may be SARAM on Zone 7 (separately addressed), can all interfaces work in parallel ?
How is your project going?
I'm working on the memory interface part of the project (FPGA-DSP via XINT, working on eZdsp). The issue of ADC channels has been solved. However, I'm looking into the analog pre-processing of the ADC inputs, especially for the inbuilt channels on F28335, by using something like INA 159. Can you suggest any reference designs for the same ?
I am glad to hear you are making progress! I've not worked much with the ADC's inside the F28335. You might try cruising around in the C2000 forum to see if there are any references there.
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