68HC11 Timing System

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68HC11 Timing System The 68HC11 timing is controlled by a crystal oscillator connected to the XTAL and EXTAL pins on the 68HC11. The E clock, which determines the time of each instruction cycle is ¼ of the crystal frequency. For the Adapt 11 evaluation board the basic clock is 8MHz and the E clock is 2 MHz. Therefore the time of each instruction cycle is 0.5 µsec. ELET 3144 R. Alba-Flores 4
The Free-Running Counter • The output of the E clock is connected to a 16-bit counter, called the TCNT register, that is at locations $100E and $100F. • TCNT is cleared at RESET. • This is a read only register. It can not be written but it will be incremented by every tick of the E clock ELET 3144 R. Alba-Flores 5
Page 1 and 2: 68HC11 Timing System ELET 3144 R. A
Page 3: Time Measuring Methods There are di
Page 7 and 8: The Prescalar • Resolution is the
Page 9 and 10: Timer Overflow Every time the TCNT
Page 11 and 12: Example 1 • The TCNT register can
Page 13 and 14: ; * Subroutine to clear TOF SUB2: L
Page 15 and 16: Input Capture Registers Input captu
Page 17 and 18: The three 16-bit TIC registers (TIC
Page 19 and 20: Example 3. The time of a falling ed
Page 21 and 22: The corresponding interrupt bit is
Page 23 and 24: ; *** This is a program to determin

68HC11 Timing System

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