Hi!
I'm currently working on interfacing two rtd converters to a TMS320F28379D MCU. I have some problems in interfacing two PGA411 rtd converters to the MCU. I would like to have access through SPI, ABZ and parallel to both the rtd. I've some questions:
1) Is it possible to use the EMIF1 in asynchronous mode of operation to read from the parallel bus? My idea was to use 4 address lines to connect to the VA0 and VA1 of the PGA411, to connect ord[0:11] and PRD to the data line and to connect INHB to EM1OE. By reading a certain address it would be possible to access to speed and position of each of the rtd. However I'm scared about bus contention during subsequent readings, because the chip select is not used. the only way that I can imagine to solve the issue is to logically and VA0 and VA1 of rtd 1 to a chip select and VA0 and VA1 of rtd to a second chip select. However this solution would introduce an additional integrated circuit. Can someone suggest me a good way to read from parallel port with minimal overhead for the processor? I read about using GPIO registers and bit masking, but I can't understand how to efficiently manage timings in this case.
2)by using 2 SPI interfaces for the RTD I only have 1 other SPI available and 2 MCBSP (that can be used as SPI). Because of the fact that I'm also implementing the EnDat interface another SPI is used. Do you think that McBSP usage in clockstop mode can give some kind of issue in interfacing other SPI devices as DAC or eeprom memories?
3) I read a lot about how to emulate chip select on SPI on this MCU. In many thread it is suggested to use GPIO instead of spiste. I'm not convinced by this solution because it needs to manage with timings. Do you think that using a decoder to route the spiste signal to the right slave and controlling it with two or more GPIO is a possible solution? In the case of two PGA411 do you think they can share the SPI bus?(no infos are given about the impedance state during SPISTE* HIGH).
(U33 in next picture is a 74AC138M that controls three eeproms and one dac)
Thanks in advance!
Edit:
I also have another question about PGA411: I already have a +15Vcc supply plane. Do you think I can directly supply the excitation amplifier with it?
I saw in the EMC compliant reference design (TIDA-00796) that a jumper allow for direct supply from the external connector. The point is that the integrated boost converter is still working. I'm scared of some fault signal if I don't connect it. Is there any register key to tell the system I'm not using the boost converter?
In the case there are no register keys do you think I can just bypass the fault connecting VEXTS to 15Vcc so that diagnostics won't see under voltage ?
