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How to know about count errors using MJT for external signals and TIN?

Latest Updated:10/14/2004

Question:

I wish to know about count errors when using multijunction timer (MJT) for external signals (TIN, TCLK input).
Also, I wish to know what the TIN input pulse width (minimum 7/2 tc (BLCK)) stipulated in the user's manual means.

Answer:

Inside the microcomputer, external signals (TIN, TCLK input) are sampled at the falling edge of the sampling CLK signal which is internally derived from BCLK by dividing it by 2, as shown below. Therefore,

  • TD(CAP1 or CAP2) =
    1 BCLK cycle (min.) at the shortest when latched into the measure register immediately after sampling,
    or 3 BCLK cycles (max.) at the largest when input could not be sampled barely in time
  • TD(CLK) =
    2 BCLK cycles (min.) at the shortest when latched into the measure register immediately after sampling,
    or 4 BCLK cycles (max.) at the largest when input could not be sampled barely in time.
Note that these are theoretically determined values, and actually include rise and fall delay times also.

The stipulated TIN input pulse width consists of the sampling period (2 BCLK cycles) of the sampling CLK signal shown in the above timing diagram plus the rise/fall delay times (including margin) (= 7/2 tc (BCLK) at minimum).

Suitable Products
32170, 32174
32171
32172, 32173