Hi
I'm thinking about using the TMS320F28004x Family for the development of a dual axis drive system with 2 absolut encoders. As far as i understood the SPI peripheral is needed (together with the CLB) to use the absolut encoder feature. Is it still posible to use 2 absolut encoders simultaniously with one SPI for normal communication?
Thanks for your help
Ah, now I see in which direction you're thinking. But I'm still a bit confused how you like to connect two encoders to one SPI.
If you have a look at the EnDat Implementation diagram I don't see a way to use two encoders with one SPI (MISO ond MOSI are both used for one Encoder). The enable signals for the two transceivers are already done with GPIO's.
Could you explain further how you would connect them to one SPI?
Thanks a lot for your effort!
Thanks for your answer. Why does the library only support one encoder? Does the hardware limit it or is it to much work to implement a library with multiple encoders. In the following document is written, that CLB should support two encoders:
http://www.ti.com/lit/wp/sway022/sway022.pdf
"In position manager solutions, coupling the CLB with a serial port creates solutions for EnDat2.2, bidirectional/serial/synchronous (BiSS), Tamagawa T-format and other serial encoder standards. The CLB on the F28004x has enough capability to implement two channels of most protocols."
I've mostly dealt with ecoders with simple one way SPI interface. For this, the following schematics should show the approach:
With the couple of Biss and EnDat encoders I've dealt with, I used SPI module directly without CLB (this was 10 years ago). It turns out that the most important feature of CLB is clock delay compensation. If you had MCU with McBSP port you could use it and generate delayed clock via external RC circuitry. You could even set delay programably via GPIO swithcable parallel capacitors. Now if you reduce the clock frequency, then you can do without clock delay compensation. In some cases you can even push the clock frequency and you can change clock polarity and clock phase settings in SPI in order to sample data in the right moments. But this is more of a hack suitable for prototyping, and I'd not recommend it for production.
Now if you can live without clock delay compensation you can use just the SPI without CLB for Biss or EnDat communication if you want to have read/write acces, you'd need to expand the shown schematics with additional transceiver for MOSI signal. But I've always managed to use only one way communication with Biss and EnDat. Maybe I just had luck with the encoders, as they were configured correctly out of the box and they did not need any write access in order to work.
Here I go again.
You do not actually need 2 GPIO. One is enough but you need external inverter to generate the other enable signal.
