• Table of Contents

8.3 Standard Timer Module

The HCS12 standard timer module is illustrated below.

Figure 8.1 HCS12 standard timer (TIM) block diagram.

The components are listed below:

• 16-bit timer counter (TCNT). Refer to 8.4 Timer Counter Register.
• Eight channels programmed for input-capture or output-compare modules. Refer to 8.5 Input-Capture Function and 8.6 Output-Compare Function.
• Each channel has a pin at Port T (I0C0 ~ I0C7).
• 11 interrupts source - 1 for timer overflow, 8 for channels, and 2 for pulse accumulator.
• A group of registers to program the system’s functions.

8.4 Timer Counter Register

The timer counter TCNT is a 16-bit register that counts form $0000 to $FFFF. In particular, there are three registers related to the operation of this register.

1. Timer System Control Register 1 (TSCR1): A register that controls the operation of the timer counter.
2. Timer System Control Register 2 (TSCR2): Another register that controls the operation of the timer counter.
3. Timer Interrupt Flag 2 Register (TFLG2): A register that controls the interrupt flag.

Programming the Timer System

To program the timer system, we must first enable the time counter. This can be done by setting the bit 7 of the TSCR1. The TEN bit allows the timer to be used.

Figure 8.2 Timer System Control register 1 (TSCR1).

Upon enabling the time counter, it also needs a clock signal to operate.