8051 Aula 02

1
8051Aula 02

• Prof Afonso Ferreira Miguel

2
Microcontrolador 8051 (MCS-51)

• Timers do MCS51
• Two 16-bit Counter/Timers
• Up counters, can interrupt on overflow.
• Counts
• CPU cycles (crystal/12).
• External input (max. half CPU rate).
• Four Operation Modes.

3
Microcontrolador 8051 (MCS-51)

• Timers do MCS51
• Timer Mode 0
• Emulates 8048 counter/timer (13-bits).
• 8-bit counter (TL0 or TL1).
• 5-bit prescaler (TH0 or TH1).
• Timer Mode 1
• Simple 16-bit counter.
• Timer Mode 2
• 8-bit auto-reload.
• Counter in TL0 or TL1.
• Reload value in TH0 or TH1.
• Provides a periodic flag or interrupt.

4
Microcontrolador 8051 (MCS-51)

• Timers do MCS51
• Timer Mode 3
• Splits timer 0 into two 8-bit counter/timers.
• First counter (TLO) acts like mode 0,
• without prescaler.
• Second counter (TH0)
• Counts CPU cycles.
• Uses TR1 (timer 1 run bit) as enable.
• Uses TF1 (timer 1 overflow bit) as flag.
• Uses Timer 1 interrupt.
• Timer 1 (when timer 0 is in mode 3 )
• Counter stopped if in mode 3.
• Running in mode 0, 1, or 2.
• Has gate (INT1) and external input (T1), but no
  flag or interrupt.
• May be used as a baud rate generator.

5
Microcontrolador 8051 (MCS-51)

• Timers do MCS51 MODO 1

Osc.
12
Osc.
Interrupt
TL1
TH1
TF1
8-bits
8-bits
T1 (Pin)
Control
TR1
Gate
INT1 (Pin)
The Gate input controls whether the Counter runs
while gated by
the interrupt signal or not.
6
Microcontrolador 8051 (MCS-51)

• Timers do MCS51 MODO 2

Osc.
12
Osc.
Interrupt
TL1
TF1
8-bits
T1 (Pin)
Control
TR1
Gate
INT1 (Pin)
The Gate input controls whether the Counter runs
while gated by
the interrupt signal or not.
7
Microcontrolador 8051 (MCS-51)

• Timers do MCS51 TMOD

8
Microcontrolador 8051 (MCS-51)

• Timers do MCS51 TCON