What is alternate function of T0 and T1 pin?

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Examoogle · Accepted Answer

Port 3

Explanation: In the 8051 microcontroller architecture, the pins $P3.4$ and $P3.5$ of Port 3 serve the dual purpose of general-purpose I/O and alternate functions for Timers. Specifically, the $T0$ pin (alternate function of $P3.4$) serves as the external clock input for Timer 0, and the $T1$ pin (alternate function of $P3.5$) serves as the external clock input for Timer 1. Working Principle: When a timer is configured in 'Counter Mode' by setting the $C/\overline{T}$ bit in the $TMOD$ register to 1, the timer increments on the negative edge of the signal applied to the corresponding $T0$ or $T1$ pin. This allows the 8051 to count external events or measure frequency by sampling external pulses through these designated pins on Port 3. Key Formulas: $C/\overline{T} = 1$ — Bit configuration in TMOD to select Counter Mode; $f_{ext} \le \frac{f_{osc}}{24}$ — Maximum frequency limit for external input pulses Key Points: Port 3 is a multifunction port providing various special features like UART, interrupts, and timers.; Timer 0 uses pin $P3.4$ ($T0$) as an external input.; Timer 1 uses pin $P3.5$ ($T1$) as an external input.; To use these as external clock inputs, the timer must be in Counter Mode ($C/\overline{T} = 1$). Advantages: Allows measurement of external pulse widths and frequencies.; Enables counting of external events such as sensor pulses or switch presses.; Reduces CPU overhead for event counting. Disadvantages: External input frequency is limited by the oscillator frequency.; Consumes specific pins of Port 3, reducing available general-purpose I/O lines. Applications: Digital tachometers for RPM measurement.; Frequency counting and pulse width measurement circuits.; Event logging in embedded systems. Additional Info: The 8051 uses $P3.0$ and $P3.1$ for Serial Communication (RXD/TXD).. The 8051 uses $P3.2$ and $P3.3$ for External Interrupts ($overline{INT0}$, $overline{INT1}$).. The 8051 uses $P3.6$ and $P3.7$ for Write/Read signals ($overline{WR}$, $overline{RD}$) during external memory access. Answer: D is correct — The pins T0 and T1 are the alternate functions of the P3.4 and P3.5 pins of Port 3 in the 8051 microcontroller. Exam Tip: Always remember that Port 3 in 8051 is the 'Special Function' port; if you need a peripheral feature like Interrupts, Serial Comms, or Timers, you look for the pins on Port 3.

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