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In an 8051 microcontroller, the PSEN signal is used to access:
Internal RAM
External Data Memory
External Program Memory
Internal SFRs
External Program Memory
The PSEN (Program Store Enable) signal is an active-low output pin on the 8051 microcontroller that acts as a read strobe to enable the external program memory. It is specifically designed to allow the microcontroller to fetch instruction codes (opcodes) from an external ROM or EPROM.
The PSEN (Program Store Enable) signal is an active-low output pin on the 8051 microcontroller that acts as a read strobe to enable the external program memory. It is specifically designed to allow the microcontroller to fetch instruction codes (opcodes) from an external ROM or EPROM.
fclkтАЛ=TcyтАЛ1тАЛ тАФ where TcyтАЛ is the machine cycle time of the 8051 architecture.
When the 8051 needs to execute a program stored in external memory, the Program Counter (PC) places the address on the address bus. The PSEN pin is then driven low, signaling the external memory device to place the instruction byte at that address onto the data bus for the CPU to read.
PSEN stands for Program Store Enable.
It is an active-low signal (PSEN=0).
It is not activated when accessing internal program memory or external data memory.
The 8051 uses the RD (Read) signal instead of PSEN to access external data memory.
Allows expansion of program memory beyond the internal 4KB limit.
Provides a dedicated strobe to prevent contention with data memory read signals.
Requires additional hardware like latches (e.g., 74LS373) for address demultiplexing.
Increases board space and component count.
Embedded systems with complex code requirements.
Systems requiring field-programmable external flash or EPROM storage.
The 8051 has 64KB of program memory addressing capability.
Option A (Internal RAM) is accessed via the MOV instructions and internal address decoders.
Option B (External Data Memory) uses the RD and WR signals, not PSEN.
Option D (Internal SFRs) are accessed directly through the internal data bus without external control signals.
C is correct тАФ PSEN is the dedicated control signal utilized by the 8051 to facilitate the retrieval of instruction bytes from external program memory.
Always distinguish between PSEN and RD: PSEN is for code memory (opcodes), whereas RD is for data memory (variables).