While designing a system using an 8051 microcontroller, the lower address byte and data are multiplexed on the same lines. Which hardware component is required to hold the lower address byte temporarily for correct memory access?
Latch
To address the problem stated in the question, we need to understand how the 8051 microcontroller handles address and data lines. In the 8051 microcontroller, the lower 8 bits of the address bus (A0-A7) are multiplexed with the data bus (D0-D7). This means both address and data appear on the same lines at different times during the operation.
To correctly access external memory, we require a mechanism to hold the lower address byte stable while the microcontroller fetches the data. This is achieved using a hardware component called a latch. The latch captures and holds the lower address byte when the Address Latch Enable (ALE) signal is active. This way, once the address is latched, the data can be sent through the same lines without confusion.
- When ALE is high, the lower address byte is available on lines and is latched into the external latch.
- When ALE goes low, data transfer occurs on the same multiplexed lines, but the address remains stable in the latch.
- The most commonly used latch in this application is the 74HC573 octal latch.
Now, let's evaluate the given options:
- Encoder: Encoders are used to convert information from one format to another, mainly used in digital circuits for converting binary data. Encoders do not serve the purpose of holding address lines.
- Multiplexer: A multiplexer is used to select one of many inputs. It is not used for holding addresses but for selecting inputs based on control signals.
- Subtractor: A subtractor is an arithmetic operation circuit used to perform subtraction, not for addressing purposes.
- Latch (Correct Answer): As explained, the latch is used to temporarily hold the lower address byte for correct memory addressing.
Hence, the correct hardware component required to hold the lower address byte temporarily for correct memory access is a latch.
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