Will replacing the 18.432MHz crystal with an 18MHz one affect the speed of anything on the TINI besides the CAN bus?

Tim Rohaly

If you change the 18.432MHz crystal, it will affect:

  • CAN baud rates
  • Serial baud rates
  • Scheduler
  • System timer (software clock)
  • 1-Wire timing
It will not affect:
  • Real-time clock
  • Ethernet controller

If you do this modification it won't affect the serial baud rates (including 1-Wire timing) enough to matter; these are far more tolerant of variation than CAN, and can work fine even with a few percent error.

Keep in mind that the 80C390 CPU is rated to only 40MHz. The CPU doubles the crystal frequency, implying that you need to keep the crystal less than 20MHz.

It has been reported on the TINI mailing list that changing the crystal to 18MHz works fine with CAN baud rates of 250 Kbps, 500 Kbps, and 1 Mbps. The serial ports are reported to function properly as well.

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