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TMS320F28030: TMS320F28030 / CANTransceiver / External oscillator

Yasuhiro Shirai
Prodigy 70 points
Part Number: TMS320F28030


Tool/software:

The microcontroller (MS320F28030) and external oscillator are behaving abnormally,and CAN communication is abnormal.

The output amplitude of the external oscillator is becoming smaller due to heat.
Based on these facts, the following assumption is made, but is it correct?

If the output amplitude of the external oscillator simply becomes smaller,

there is no fluctuation in the input frequency, so no abnormality occurs in CAN communication.

If the output amplitude repeatedly increases and decreases, the number of inputs will fluctuate,

causing bit shifts in CAN communication and error frames.

If there are many error frames, the "Bus-off" state will occur.
When an oscilloscope is connected to obtain the raw waveform of the

external oscillator, the signal form changes and it cannot be measured.

  • 0
    TI__Guru**** 197446 points

    Hi Yasuhiro,

    Low amplitude means low energy flow and therefore low energy consumption, so it is desirable. How small is the Vpp (peak-2-peak)? The peak-to-peak amplitude can be significantly smaller than the supply voltage. The on-chip crystal oscillator X1 and X2 pins are 1.8-V level signal.

    The crystal voltage can be measured at X1 using an active probe with low capacitive load and high impedance

    Correct operation of the crystal oscillator is dependent on the values of the two external capacitors, CL1 and CL2. These capacitors together with any parasitic capacitance in the PCB and the crystal terminals compose the total load capacitance seen by the crystal. The optimum load capacitance for the crystal, CL, is given in the crystal datasheet and CL1 and CL2 should be matched to this value. If CL1=CL2, CL1=CL2= 2*CL