Which control function use during programming of internal EPROM?

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$ALE / PROG$

Explanation: In the 8051 microcontroller, the ALE/\overline{PROG} pin serves a dual purpose. During normal operation, it functions as the Address Latch Enable signal, but during the EPROM programming mode, it acts as the input for the programming pulse (active low) used to store code into the internal memory. Working Principle: When the microcontroller is in programming mode, the \overline{EA} pin is held at a high voltage level (typically 12V for Vpp). The programming process involves applying the byte to be programmed on the P0 port, setting the address on P1 and lower P2 pins, and then applying a low-going pulse to the ALE/\overline{PROG} pin to trigger the internal EPROM write cycle. Key Formulas: $V_{PP} = 12V$ — Programming voltage required for internal EPROM; $t_{prog} = 50ms$ — Typical duration of the programming pulse Key Points: ALE stands for Address Latch Enable, used to latch low-order address bits.; The \overline{PROG} function is activated only when the device is in Programming Mode.; The 8051 must be in a specific state (EA pin at 12V) to accept pulses on the \overline{PROG} pin.; Internal EPROM programming is non-volatile. Advantages: Allows field programmability for small-scale production.; Consolidates dual functionality onto a single pin to save PCB space. Disadvantages: Requires high voltage (12V) which can stress components if not regulated.; The EPROM version is generally not as flexible as Flash-based variants like the 89C51. Applications: Embedded system firmware burning.; Initial manufacturing configuration of 8051-based products. Additional Info: The \overline{EA} (External Access) pin determines whether the device fetches code from internal or external memory; holding it at 12V prepares the internal memory for programming.. Option B (RESET) is used to initialize the internal state, not for memory programming.. Option C (\overline{EA}/Vpp) is the input for the programming voltage level, not the control pulse itself. Answer: A is correct — The ALE/\overline{PROG} pin is used to supply the low-active programming pulse during the EPROM writing process. Exam Tip: Always distinguish between voltage requirements (like Vpp) and timing/control signals (like \overline{PROG}) in microcontroller programming. Vpp provides the energy, while \overline{PROG} acts as the 'write' trigger.

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