Samsung KS57C2308 manual TC0 Programmable TIMER/COUNTER Function, TC0 Operation Sequence

KS57C2308/P2308/C2316/P2316 TIMERS and TIMER/COUNTERS

TC0 PROGRAMMABLE TIMER/COUNTER FUNCTION

Timer/counter 0 can be programmed to generate interrupt requests at various intervals based on the selected system clock frequency. Its 8-bit TC0 mode register TMOD0 is used to activate the timer/counter and to select the clock frequency.

The reference register TREF0 stores the value for the number of clock pulses to be generated between interrupt requests. The counter register, TCNT0, counts the incoming clock pulses, which are compared to the TREF0 value as TCNT0 is incremented. When there is a match (TREF0 = TCNT0), an interrupt request is generated.

To program timer/counter 0 to generate interrupt requests at specific intervals, choose one of four internal clock frequencies (divisions of the system clock, fxx) and load a counter reference value into the TREF0 register. TCNT0 is incremented each time an internal counter pulse is detected with the reference clock frequency specified by TMOD0.4–TMOD0.6 settings.

To generate an interrupt request, the TC0 interrupt request flag (IRQT0) is set to logic one, the status of TOL0 is inverted, and the interrupt is generated. The content of TCNT0 is then cleared to 00H and TC0 continues counting. The interrupt request mechanism for TC0 includes an interrupt enable flag (IET0) and an interrupt request flag (IRQT0).

TC0 OPERATION SEQUENCE

The general sequence of operations for using TC0 can be summarized as follows:

1.Set TMOD0.2 to "1" to enable TC0.

2.Set TMOD0.6 to "1" to enable the system clock (fxx) input.

3.Set TMOD0.5 and TMOD0.4 bits to desired internal frequency (fxx/2n).

4.Load a value to TREF0 to specify the interval between interrupt requests.

5.Set the TC0 interrupt enable flag (IET0) to "1".

6.Set TMOD0.3 bit to "1" to clear TCNT0, IRQT0, and TOL0, and start counting.

7.TCNT0 increments with each internal clock pulse.

8.When the comparator shows TCNT0 = TREF0, the IRQT0 flag is set to "1" and an interrupt request is generated.

9.Output latch (TOL0) logic toggles high or low.

10.TCNT0 is cleared to 00H and counting resumes.

11.Programmable timer/counter operation continues until TMOD0.2 is cleared to "0".

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