How to Use Timer-0 of AT89C51 in Mode-0 (13-bit mode)

When the timer-0 is in 13-bit mode, the timer can only contains 8192 values. It will overflow back to zero after 8192 counts. In this mode, 0-4 bits of TL0 register and 0-7 bits of TH0 register are used.

1.1 Initialization

The following function initialize the timer-0 in mode-0 with internal ON/OFF control configuration.

void InitTimer0Mode0(void)
{
// reset timer-0 higher byte register
TH0 = 0x00;
// reset timer-0 lower byte register
TL0 = 0x00;
// GATE1– C/T1– T1M1– T1M0– GATE0– C/T0– T0M1– T0M0
//      0              0            0              0               0               0            0              0
TMOD = 0x00;
}

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1.2 Start Timer

The following function start timer-0 from software.

void StartTimer0(void)
{
// set timer-0 run bit (in TCON register)
TR0 = 1;
}

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1.3 Stop Timer

The following function stop timer-0 from software.

void StopTimer0(void)
{
// reset timer-0 run bit (in TCON register)
TR0 = 0;
}

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1.4 Monitor Timer-0 Overflow

The following function monitor overflow of timer-0 in mode-0. It return set bit when timer-0 is overflow.

bit MonOverFlowTimer0(void)
{
// this bit is set by controller when timer value
// reach its maximum value 8192
return TF0;
}

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1.5 Reset Timer-0 Overflow Bit

As timer-0 overflow bit is set automatically by the controller but it has to be reset manually. The following function reset the overflow bit of timer-0.

void ResetOverFlowBitTimer0(void)
{
// this bit is clear manually
TF0 = 0;
}

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1.6 Pre-Set Timer-0 Registers

You can load maximum 8191 value in the timer-0 data registers. If you load 2000 value in the timer-0 registers, it means timer will overflow after 2000 timer pulses. In the following function you can pass up to 8192 value.

void SetValTimer0Mode0(unsigned int tick_val)
{
unsigned int val = 8192 – tick_val;
TH0 = val / 32;
TL0 = val % 32;
}

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1.7 Download APIs

You can download complete set of APIs here.

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1.8 Example of Timer-0 Mode-0 (Software ON/OFF)

This example toggles the port-1 of controller with a timer cycle delay. You are free to reuse anywhere and can be download complete project here.

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1.9 Example of Timer-0 Mode-0 (External ON/OFF)

This example toggles the port-1 of controller with a timer cycle delay, but the timer ON/OFF control is from external. When P3.2 (INT0) bit is high then timer-0 is start and when this bit is low then timer-0 is off. Only the GATE0 bit is set in TMOD register. The following function initialize the timer-0 in mode-0 with external ON/OFF control.

void InitTimer0Mode0(void)
{
// reset timer-0 higher byte register
TH0 = 0x00;
// reset timer-0 lower byte register
TL0 = 0x00;
// GATE1– C/T1– T1M1– T1M0– GATE0– C/T0– T0M1– T0M0
//      0              0            0              0               1               0            0              0
TMOD = 0x08;
}

You are free to reuse anywhere and can be download complete project here.