Posted on May 17, 2011 at 13:05I was just about to order PCBs for my first design with the STM32, and then I saw the data sheet for the STM32F107, with ethernet. I have (barely) enough free pins that I can reshuffle things and use RMII hooked up to a PHY. My plan is to still leave the serial and CAN interfaces in place, so I'm not out anything if the ethernet doesn't work, and I can use the F103 until the F107 is available.
I checked ST's website, and I don't see any example schematics or eval board schematics I can clone. They do have drawings at the end of the 'F107 data sheet, Appendix A, pages 83-85 and 87-88, that show various configurations. Right now I'm planning on using page 85, ''RMII with a 25MHz crystal'', but I'm unsure how the 50MHz clock is supposed to be generated by the STM32.
Can I use any timer pin? Or do I have to use the ''MCO'' (shown on the Figure 50 example on page 87)? The main reason I picked ''RMII with a 25MHz crystal'' is because it had a part-number for a PHY to use, which is one less thing for me to worry about. ''RMII with a 50MHz oscillator'' would be okay by me too, if anyone would like to suggest a PHY and oscillator part. Or else will the DP83848 work with a 50MHz oscillator vs. having the STM32 PLL it off of the 25MHz crystal? I don't mind the extra cost of an oscillator vs. a crystal if it adds robustness (crystal startup issues are sometimes problematic and a PITA to trackdown), but I really don't know if oscillators are any better than crystals.
Thanks,
Miles
